Menu
Search

Library Reference

version 2.109.1

overview

Report a bug
If you spot a problem with this page, click here to create a Bugzilla issue.
Improve this page
Quickly fork, edit online, and submit a pull request for this page. Requires a signed-in GitHub account. This works well for small changes. If you'd like to make larger changes you may want to consider using a local clone.

std.checkedint

This module defines facilities for efficient checking of integral operations against overflow, casting with loss of precision, unexpected change of sign, etc. The checking (and possibly correction) can be done at operation level, for example opChecked!"+"(x, y, overflow) adds two integrals x and y and sets overflow to true if an overflow occurred. The flag overflow (a bool passed by reference) is not touched if the operation succeeded, so the same flag can be reused for a sequence of operations and tested at the end.
Issuing individual checked operations is flexible and efficient but often tedious. The Checked facility offers encapsulated integral wrappers that do all checking internally and have configurable behavior upon erroneous results. For example, Checked!int is a type that behaves like int but aborts execution immediately whenever involved in an operation that produces the arithmetically wrong result. The accompanying convenience function checked uses type deduction to convert a value x of integral type T to Checked!T by means of checked(x). For example: 
void main()
{
    import std.checkedint, std.stdio;
    writeln((checked(5) + 7).get); // 12
    writeln((checked(10) * 1000 * 1000 * 1000).get); // Overflow
}
Similarly, checked(-1) > uint(0) aborts execution (even though the built-in comparison int(-1) > uint(0) is surprisingly true due to language's conversion rules modeled after C). Thus, Checked!int is a virtually drop-in replacement for int useable in debug builds, to be replaced by int in release mode if efficiency demands it.
Checked has customizable behavior with the help of a second type parameter, Hook. Depending on what methods Hook defines, core operations on the underlying integral may be verified for overflow or completely redefined. If Hook defines no method at all and carries no state, there is no change in behavior, i.e. Checked!(int, void) is a wrapper around int that adds no customization at all.
This module provides a few predefined hooks (below) that add useful behavior to Checked:
Abort fails every incorrect operation with a message to std.stdio. stderr followed by a call to assert(0). It is the default second parameter, i.e. Checked!short is the same as Checked!(short, Abort).
Throw fails every incorrect operation by throwing an exception.
Warn prints incorrect operations to std.stdio.stderr but otherwise preserves the built-in behavior.
ProperCompare fixes the comparison operators ==, !=, <, <=, >, and >= to return correct results in all circumstances, at a slight cost in efficiency. For example, Checked!(uint, ProperCompare)(1) > -1 is true, which is not the case for the built-in comparison. Also, comparing numbers for equality with floating-point numbers only passes if the integral can be converted to the floating-point number precisely, so as to preserve transitivity of equality.
WithNaN reserves a special "Not a Number" (NaN) value akin to the homonym value reserved for floating-point values. Once a Checked!(X, WithNaN) gets this special value, it preserves and propagates it until reassigned. isNaN can be used to query whether the object is not a number.
Saturate implements saturating arithmetic, i.e. Checked!(int, Saturate) "stops" at int.max for all operations that would cause an int to overflow toward infinity, and at int.min for all operations that would correspondingly overflow toward negative infinity.
These policies may be used alone, e.g. Checked!(uint, WithNaN) defines a uint-like type that reaches a stable NaN state for all erroneous operations. They may also be "stacked" on top of each other, owing to the property that a checked integral emulates an actual integral, which means another checked integral can be built on top of it. Some combinations of interest include:
Checked!(Checked!int, ProperCompare)
defines an int with fixed comparison operators that will fail with assert(0) upon overflow. (Recall that Abort is the default policy.) The order in which policies are combined is important because the outermost policy (ProperCompare in this case) has the first crack at intercepting an operator. The converse combination Checked!(Checked!(int, ProperCompare)) is meaningless because Abort will intercept comparison and will fail without giving ProperCompare a chance to intervene.
Checked!(Checked!(int, ProperCompare), WithNaN)
defines an int-like type that supports a NaN value. For values that are not NaN, comparison works properly. Again the composition order is important; Checked!(Checked!(int, WithNaN), ProperCompare) does not have good semantics because ProperCompare intercepts comparisons before the numbers involved are tested for NaN.
The hook's members are looked up statically in a Design by Introspection manner and are all optional. The table below illustrates the members that a hook type may define and their influence over the behavior of the Checked type using it. In the table, hook is an alias for Hook if the type Hook does not introduce any state, or an object of type Hook otherwise.
Hook member Semantics in Checked!(T, Hook)
defaultValue If defined, Hook.defaultValue!T is used as the default initializer of the payload.
min If defined, Hook.min!T is used as the minimum value of the payload.
max If defined, Hook.max!T is used as the maximum value of the payload.
hookOpCast If defined, hook.hookOpCast!U(get) is forwarded to unconditionally when the payload is to be cast to type U.
onBadCast If defined and hookOpCast is not defined, onBadCast!U(get) is forwarded to when the payload is to be cast to type U and the cast would lose information or force a change of sign.
hookOpEquals If defined, hook.hookOpEquals(get, rhs) is forwarded to unconditionally when the payload is compared for equality against value rhs of integral, floating point, or Boolean type.
hookOpCmp If defined, hook.hookOpCmp(get, rhs) is forwarded to unconditionally when the payload is compared for ordering against value rhs of integral, floating point, or Boolean type.
hookOpUnary If defined, hook.hookOpUnary!op(get) (where op is the operator symbol) is forwarded to for unary operators - and ~. In addition, for unary operators ++ and --, hook.hookOpUnary!op(payload) is called, where payload is a reference to the value wrapped by Checked so the hook can change it.
hookOpBinary If defined, hook.hookOpBinary!op(get, rhs) (where op is the operator symbol and rhs is the right-hand side operand) is forwarded to unconditionally for binary operators +, -, *, /, %, ^^, &, |, ^, <<, >>, and >>>.
hookOpBinaryRight If defined, hook.hookOpBinaryRight!op(lhs, get) (where op is the operator symbol and lhs is the left-hand side operand) is forwarded to unconditionally for binary operators +, -, *, /, %, ^^, &, |, ^, <<, >>, and >>>.
onOverflow If defined, hook.onOverflow!op(get) is forwarded to for unary operators that overflow but only if hookOpUnary is not defined. Unary ~ does not overflow; unary - overflows only when the most negative value of a signed type is negated, and the result of the hook call is returned. When the increment or decrement operators overflow, the payload is assigned the result of hook.onOverflow!op(get). When a binary operator overflows, the result of hook.onOverflow!op(get, rhs) is returned, but only if Hook does not define hookOpBinary.
hookOpOpAssign If defined, hook.hookOpOpAssign!op(payload, rhs) (where op is the operator symbol and rhs is the right-hand side operand) is forwarded to unconditionally for binary operators +=, -=, *=, /=, %=, ^^=, &=, |=, ^=, <<=, >>=, and >>>=.
onLowerBound If defined, hook.onLowerBound(value, bound) (where value is the value being assigned) is forwarded to when the result of binary operators +=, -=, *=, /=, %=, ^^=, &=, |=, ^=, <<=, >>=, and >>>= is smaller than the smallest value representable by T.
onUpperBound If defined, hook.onUpperBound(value, bound) (where value is the value being assigned) is forwarded to when the result of binary operators +=, -=, *=, /=, %=, ^^=, &=, |=, ^=, <<=, >>=, and >>>= is larger than the largest value representable by T.
hookToHash If defined, hook.hookToHash(payload) (where payload is a reference to the value wrapped by Checked) is forwarded to when toHash is called on a Checked type. Custom hashing can be implemented in a Hook, otherwise the built-in hashing is used.

Source std/checkedint.d

Examples: 
int[] concatAndAdd(int[] a, int[] b, int offset)
{
    // Aborts on overflow on size computation
    auto r = new int[(checked(a.length) + b.length).get];
    // Aborts on overflow on element computation
    foreach (i; 0 .. a.length)
        r[i] = (a[i] + checked(offset)).get;
    foreach (i; 0 .. b.length)
        r[i + a.length] = (b[i] + checked(offset)).get;
    return r;
}
writeln(concatAndAdd([1, 2, 3], [4, 5], -1)); // [0, 1, 2, 3, 4]
Examples:
Saturate stops at an overflow 
auto x = (cast(byte) 127).checked!Saturate;
writeln(x); // 127
x++;
writeln(x); // 127
Examples:
WithNaN has a special "Not a Number" (NaN) value akin to the homonym value reserved for floating-point values 
auto x = 100.checked!WithNaN;
writeln(x); // 100
x /= 0;
assert(x.isNaN);
Examples:
ProperCompare fixes the comparison operators ==, !=, <, <=, >, and >= to return correct results 
uint x = 1;
auto y = x.checked!ProperCompare;
assert(x < -1); // built-in comparison
assert(y > -1); // ProperCompare
Examples:
Throw fails every incorrect operation by throwing an exception 
import std.exception : assertThrown;
auto x = -1.checked!Throw;
assertThrown(x / 0);
assertThrown(x + int.min);
assertThrown(x == uint.max);
struct Checked(T, Hook = Abort) if (isIntegral!T || is(T == Checked!(U, H), U, H));
Checked integral type wraps an integral T and customizes its behavior with the help of a Hook type. The type wrapped must be one of the predefined integrals (unqualified), or another instance of Checked.
Parameters:
T type that is wrapped in the Checked type
Hook hook type that customizes the behavior of the Checked type
Examples: 
// Hook that ignores all problems.
static struct Ignore
{
    @nogc nothrow pure @safe static:
    Dst onBadCast(Dst, Src)(Src src) { return cast(Dst) src; }
    Lhs onLowerBound(Rhs, T)(Rhs rhs, T bound) { return cast(T) rhs; }
    T onUpperBound(Rhs, T)(Rhs rhs, T bound) { return cast(T) rhs; }
    bool hookOpEquals(Lhs, Rhs)(Lhs lhs, Rhs rhs) { return lhs == rhs; }
    int hookOpCmp(Lhs, Rhs)(Lhs lhs, Rhs rhs) { return (lhs > rhs) - (lhs < rhs); }
    typeof(~Lhs()) onOverflow(string x, Lhs)(ref Lhs lhs) { return mixin(x ~ "lhs"); }
    typeof(Lhs() + Rhs()) onOverflow(string x, Lhs, Rhs)(Lhs lhs, Rhs rhs)
    {
        static if (x == "/")
            return typeof(lhs / rhs).min;
        else
            return mixin("lhs" ~ x ~ "rhs");
    }
}

auto x = Checked!(int, Ignore)(5) + 7;
alias Representation = T;
The type of the integral subject to checking.
Hook hook;
hook is a member variable if it has state, or an alias for Hook otherwise.
inout auto get();
Returns:
A copy of the underlying value.
Examples: 
auto x = checked(ubyte(42));
static assert(is(typeof(x.get()) == ubyte));
writeln(x.get); // 42
const y = checked(ubyte(42));
static assert(is(typeof(y.get()) == const ubyte));
writeln(y.get); // 42
enum Checked!(T, Hook) min;

enum Checked!(T, Hook) max;
Defines the minimum and maximum. These values are hookable by defining Hook.min and/or Hook.max.
Examples:
Defines the minimum and maximum. These values are hookable by defining Hook.min and/or Hook.max. 
writeln(Checked!short.min); // -32768
writeln(Checked!(short, WithNaN).min); // -32767
writeln(Checked!(uint, WithNaN).max); // uint.max - 1
this(U)(U rhs)
if (valueConvertible!(U, T) || !isIntegral!T && is(typeof(T(rhs))) || is(U == Checked!(V, W), V, W) && is(typeof(Checked!(T, Hook)(rhs.get))));
Constructor taking a value properly convertible to the underlying type. U may be either an integral that can be converted to T without a loss, or another Checked instance whose representation may be in turn converted to T without a loss.
Examples: 
auto a = checked(42L);
writeln(a); // 42
auto b = Checked!long(4242); // convert 4242 to long
writeln(b); // 4242
ref Checked opAssign(U)(U rhs) return
if (is(typeof(Checked!(T, Hook)(rhs))));
Assignment operator. Has the same constraints as the constructor.
Parameters:
U rhs The value to assign
Returns:
A reference to this
Examples: 
Checked!long a;
a = 42L;
writeln(a); // 42
a = 4242;
writeln(a); // 4242
Examples: 
Checked!long a, b;
a = b = 3;
assert(a == 3 && b == 3);
this(Range)(Range str)
if (isInputRange!Range && isSomeChar!(ElementType!Range));
Construct from a decimal string. The conversion follows the same rules as std.conv.to converting a string to the wrapped T type.
Parameters:
Range str an input range of characters
Examples:
std.conv.to can convert a string to a Checked!T: 
import std.conv : to;

const a = to!long("1234");
const b = to!(Checked!long)("1234");
writeln(a); // b
U opCast(U, this _)()
if (isIntegral!U || isFloatingPoint!U || is(U == bool));
Casting operator to integral, bool, or floating point type.
If a cast to a floating-point type is requested and Hook defines onBadCast, the cast is verified by ensuring get == cast(T) U(get). If that is not true, hook.onBadCast!U(get) is returned.
If a cast to an integral type is requested and Hook defines onBadCast, the cast is verified by ensuring get and cast(U) get are the same arithmetic number. (Note that int(-1) and uint(1) are different values arithmetically although they have the same bitwise representation and compare equal by language rules.) If the numbers are not arithmetically equal, hook.onBadCast!U(get) is returned.
Parameters:
U The type to cast to
Returns:
If Hook defines hookOpCast, the call immediately returns hook.hookOpCast!U(get). Otherwise, casting to bool yields get != 0 and casting to another integral that can represent all values of T returns get promoted to U.
Examples: 
writeln(cast(uint)checked(42)); // 42
writeln(cast(uint)checked!WithNaN(-42)); // uint.max
bool opEquals(U, this _)(U rhs)
if (isIntegral!U || isFloatingPoint!U || is(U == bool) || is(U == Checked!(V, W), V, W) && is(typeof(this == rhs.payload)));
Compares this against rhs for equality.
If U is also an instance of Checked, both hooks (left- and right-hand side) are introspected for the method hookOpEquals. If both define it, priority is given to the left-hand side.
Parameters:
U rhs Right-hand side to compare for equality
Returns:
If Hook defines hookOpEquals, the function forwards to hook.hookOpEquals(get, rhs). Otherwise, the result of the built-in operation get == rhs is returned.
Examples: 
import std.traits : isUnsigned;

static struct MyHook
{
    static bool thereWereErrors;
    static bool hookOpEquals(L, R)(L lhs, R rhs)
    {
        if (lhs != rhs) return false;
        static if (isUnsigned!L && !isUnsigned!R)
        {
            if (lhs > 0 && rhs < 0) thereWereErrors = true;
        }
        else static if (isUnsigned!R && !isUnsigned!L)
            if (lhs < 0 && rhs > 0) thereWereErrors = true;
        // Preserve built-in behavior.
        return true;
    }
}
auto a = checked!MyHook(-42);
writeln(a); // uint(-42)
assert(MyHook.thereWereErrors);
MyHook.thereWereErrors = false;
writeln(checked!MyHook(uint(-42))); // -42
assert(MyHook.thereWereErrors);
static struct MyHook2
{
    static bool hookOpEquals(L, R)(L lhs, R rhs)
    {
        return lhs == rhs;
    }
}
MyHook.thereWereErrors = false;
writeln(checked!MyHook2(uint(-42))); // a
// Hook on left hand side takes precedence, so no errors
assert(!MyHook.thereWereErrors);
const nothrow @safe size_t toHash();

shared const nothrow @safe size_t toHash(this _)();
Generates a hash for this. If Hook defines hookToHash, the call immediately returns hook.hookToHash(payload). If Hook does not implement hookToHash, but it has state, a hash will be generated for the Hook using the built-in function and it will be xored with the hash of the payload.
Returns:
The hash of this instance.
const void toString(Writer, Char)(ref scope Writer sink, ref scope const FormatSpec!Char fmt);
Writes a string representation of this to a sink.
Parameters:
Writer sink A Char accepting output range.
FormatSpec!Char fmt A std.format.FormatSpec which controls how this is formatted.
Examples:
toString is rarely directly invoked; the usual way of using it is via std.format.format: 
import std.format;

writeln(format("%04d", checked(15))); // "0015"
writeln(format("0x%02x", checked(15))); // "0x0f"
auto opCmp(U, this _)(const U rhs)
if (isIntegral!U || isFloatingPoint!U || is(U == bool));

auto opCmp(U, Hook1, this _)(Checked!(U, Hook1) rhs);
Compares this against rhs for ordering. If Hook defines hookOpCmp, the function forwards to hook.hookOpCmp(get, rhs). Otherwise, the result of the built-in comparison operation is returned.
If U is also an instance of Checked, both hooks (left- and right-hand side) are introspected for the method hookOpCmp. If both define it, priority is given to the left-hand side.
Parameters:
U rhs The right-hand side operand
U either the type of rhs or the underlying type if rhs is a Checked instance
Hook1 If rhs is a Checked instance, Hook1 represents the instance's behavior hook
Returns:
The result of hookOpCmp if hook defines hookOpCmp. If U is an instance of Checked and hook does not define hookOpCmp, result of rhs.hook.hookOpCmp is returned. If none of the instances specify the behavior via hookOpCmp, -1 is returned if lhs is lesser than rhs, 1 if lhs is greater than rhs and 0 on equality.
Examples: 
import std.traits : isUnsigned;

static struct MyHook
{
    static bool thereWereErrors;
    static int hookOpCmp(L, R)(L lhs, R rhs)
    {
        static if (isUnsigned!L && !isUnsigned!R)
        {
            if (rhs < 0 && rhs >= lhs)
                thereWereErrors = true;
        }
        else static if (isUnsigned!R && !isUnsigned!L)
        {
            if (lhs < 0 && lhs >= rhs)
                thereWereErrors = true;
        }
        // Preserve built-in behavior.
        return lhs < rhs ? -1 : lhs > rhs;
    }
}
auto a = checked!MyHook(-42);
assert(a > uint(42));
assert(MyHook.thereWereErrors);
static struct MyHook2
{
    static int hookOpCmp(L, R)(L lhs, R rhs)
    {
        // Default behavior
        return lhs < rhs ? -1 : lhs > rhs;
    }
}
MyHook.thereWereErrors = false;
assert(Checked!(uint, MyHook2)(uint(-42)) <= a);
//assert(Checked!(uint, MyHook2)(uint(-42)) >= a);
// Hook on left hand side takes precedence, so no errors
assert(!MyHook.thereWereErrors);
assert(a <= Checked!(uint, MyHook2)(uint(-42)));
assert(MyHook.thereWereErrors);
auto opUnary(string op, this _)()
if (op == "+" || op == "-" || op == "~");

ref Checked opUnary(string op)() return
if (op == "++" || op == "--");
Defines unary operators +, -, ~, ++, and --. Unary + is not overridable and always has built-in behavior (returns this). For the others, if Hook defines hookOpUnary, opUnary forwards to Checked!(typeof(hook.hookOpUnary!op(get)), Hook)(hook.hookOpUnary!op(get)).
If Hook does not define hookOpUnary but defines onOverflow, opUnary forwards to hook.onOverflow!op(get) in case an overflow occurs. For ++ and --, the payload is assigned from the result of the call to onOverflow.
Note that unary - is considered to overflow if T is a signed integral of 32 or 64 bits and is equal to the most negative value. This is because that value has no positive negation.
Parameters:
op The unary operator
Returns:
A Checked instance representing the result of the unary operation
Examples: 
static struct MyHook
{
    static bool thereWereErrors;
    static L hookOpUnary(string x, L)(L lhs)
    {
        if (x == "-" && lhs == -lhs) thereWereErrors = true;
        return -lhs;
    }
}
auto a = checked!MyHook(long.min);
writeln(a); // -a
assert(MyHook.thereWereErrors);
auto b = checked!void(42);
writeln(++b); // 43
auto opBinary(string op, Rhs)(const Rhs rhs)
if (isIntegral!Rhs || isFloatingPoint!Rhs || is(Rhs == bool));

const auto opBinary(string op, Rhs)(const Rhs rhs)
if (isIntegral!Rhs || isFloatingPoint!Rhs || is(Rhs == bool));

auto opBinary(string op, U, Hook1)(Checked!(U, Hook1) rhs);

const auto opBinary(string op, U, Hook1)(Checked!(U, Hook1) rhs);
Defines binary operators +, -, *, /, %, ^^, &, |, ^, <<, >>, and >>>. If Hook defines hookOpBinary, opBinary forwards to Checked!(typeof(hook.hookOpBinary!op(get, rhs)), Hook)(hook.hookOpBinary!op(get, rhs)).
If Hook does not define hookOpBinary but defines onOverflow, opBinary forwards to hook.onOverflow!op(get, rhs) in case an overflow occurs.
If two Checked instances are involved in a binary operation and both define hookOpBinary, the left-hand side hook has priority. If both define onOverflow, a compile-time error occurs.
Parameters:
op The binary operator
Rhs rhs The right hand side operand
U If rhs is a Checked instance, U represents the underlying instance type
Hook1 If rhs is a Checked instance, Hook1 represents the instance's behavior hook
Returns:
A Checked instance representing the result of the binary operation
auto opBinaryRight(string op, Lhs)(const Lhs lhs)
if (isIntegral!Lhs || isFloatingPoint!Lhs || is(Lhs == bool));

const auto opBinaryRight(string op, Lhs)(const Lhs lhs)
if (isIntegral!Lhs || isFloatingPoint!Lhs || is(Lhs == bool));
Defines binary operators +, -, *, /, %, ^^, &, |, ^, <<, >>, and >>> for the case when a built-in numeric or Boolean type is on the left-hand side, and a Checked instance is on the right-hand side.
Parameters:
op The binary operator
Lhs lhs The left hand side operand
Returns:
A Checked instance representing the result of the binary operation
ref Checked opOpAssign(string op, Rhs)(const Rhs rhs) return
if (isIntegral!Rhs || isFloatingPoint!Rhs || is(Rhs == bool));

ref Checked opOpAssign(string op, Rhs)(const Rhs rhs) return
if (is(Rhs == Checked!(RhsT, RhsHook), RhsT, RhsHook));
Defines operators +=, -=, *=, /=, %=, ^^=, &=, |=, ^=, <<=, >>=, and >>>=.
If Hook defines hookOpOpAssign, opOpAssign forwards to hook.hookOpOpAssign!op(payload, rhs), where payload is a reference to the internally held data so the hook can change it.
Otherwise, the operator first evaluates auto result = opBinary!op(payload, rhs).payload, which is subject to the hooks in opBinary. Then, if result is less than Checked!(T, Hook).min and if Hook defines onLowerBound, the payload is assigned from hook.onLowerBound(result, min). If result is greater than Checked!(T, Hook).max and if Hook defines onUpperBound, the payload is assigned from hook.onUpperBound(result, min).
If the right-hand side is also a Checked but with a different hook or underlying type, the hook and underlying type of this Checked takes precedence.
In all other cases, the built-in behavior is carried out.
Parameters:
op The operator involved (without the "=", e.g. "+" for "+=" etc)
Rhs rhs The right-hand side of the operator (left-hand side is this)
Returns:
A reference to this.
Examples: 
static struct MyHook
{
    static bool thereWereErrors;
    static T onLowerBound(Rhs, T)(Rhs rhs, T bound)
    {
        thereWereErrors = true;
        return bound;
    }
    static T onUpperBound(Rhs, T)(Rhs rhs, T bound)
    {
        thereWereErrors = true;
        return bound;
    }
}
auto x = checked!MyHook(byte.min);
x -= 1;
assert(MyHook.thereWereErrors);
MyHook.thereWereErrors = false;
x = byte.max;
x += 1;
assert(MyHook.thereWereErrors);
Checked!(T, Hook) checked(Hook = Abort, T)(const T value)
if (is(typeof(Checked!(T, Hook)(value))));
Convenience function that turns an integral into the corresponding Checked instance by using template argument deduction. The hook type may be specified (by default Abort).
Parameters:
Hook type that customizes the behavior, by default Abort
T type represetinfg the underlying represantion of the Checked instance
T value the actual value of the representation
Returns:
A Checked instance customized by the provided Hook and value
Examples: 
static assert(is(typeof(checked(42)) == Checked!int));
writeln(checked(42)); // Checked!int(42)
static assert(is(typeof(checked!WithNaN(42)) == Checked!(int, WithNaN)));
writeln(checked!WithNaN(42)); // Checked!(int, WithNaN)(42)
struct Abort;
Force all integral errors to fail by printing an error message to stderr and then abort the program. Abort is the default second argument for Checked.
Examples: 
void test(T)()
{
    Checked!(int, Abort) x;
    x = 42;
    auto x1 = cast(T) x;
    writeln(x1); // 42
    //x1 += long(int.max);
}
test!short;
test!(const short);
test!(immutable short);
Dst onBadCast(Dst, Src)(Src src);
Called automatically upon a bad cast (one that loses precision or attempts to convert a negative value to an unsigned type). The source type is Src and the destination type is Dst.
Parameters:
Src src Souce operand
Returns:
Nominally the result is the desired value of the cast operation, which will be forwarded as the result of the cast. For Abort, the function never returns because it aborts the program.
T onLowerBound(Rhs, T)(Rhs rhs, T bound);

T onUpperBound(Rhs, T)(Rhs rhs, T bound);
Called automatically upon a bounds error.
Parameters:
Rhs rhs The right-hand side value in the assignment, after the operator has been evaluated
T bound The value of the bound being violated
Returns:
Nominally the result is the desired value of the operator, which will be forwarded as result. For Abort, the function never returns because it aborts the program.
bool hookOpEquals(Lhs, Rhs)(Lhs lhs, Rhs rhs);
Called automatically upon a comparison for equality. In case of a erroneous comparison (one that would make a signed negative value appear equal to an unsigned positive value), this hook issues assert(0) which terminates the application.
Parameters:
Lhs lhs The first argument of Checked, e.g. int if the left-hand side of the operator is Checked!int
Rhs rhs The right-hand side type involved in the operator
Returns:
Upon a correct comparison, returns the result of the comparison. Otherwise, the function terminates the application so it never returns.
int hookOpCmp(Lhs, Rhs)(Lhs lhs, Rhs rhs);
Called automatically upon a comparison for ordering using one of the operators <, <=, >, or >=. In case the comparison is erroneous (i.e. it would make a signed negative value appear greater than or equal to an unsigned positive value), then application is terminated with assert(0). Otherwise, the three-state result is returned (positive if lhs > rhs, negative if lhs < rhs, 0 otherwise).
Parameters:
Lhs lhs The first argument of Checked, e.g. int if the left-hand side of the operator is Checked!int
Rhs rhs The right-hand side type involved in the operator
Returns:
For correct comparisons, returns a positive integer if lhs > rhs, a negative integer if lhs < rhs, 0 if the two are equal. Upon a mistaken comparison such as int(-1) < uint(0), the function never returns because it aborts the program.
typeof(~Lhs()) onOverflow(string x, Lhs)(Lhs lhs);

typeof(Lhs() + Rhs()) onOverflow(string x, Lhs, Rhs)(Lhs lhs, Rhs rhs);
Called automatically upon an overflow during a unary or binary operation.
Parameters:
x The operator, e.g. -
Lhs lhs The left-hand side (or sole) argument
Rhs rhs The right-hand side type involved in the operator
Returns:
Nominally the result is the desired value of the operator, which will be forwarded as result. For Abort, the function never returns because it aborts the program.
struct Throw;
Force all integral errors to fail by throwing an exception of type Throw.CheckFailure. The message coming with the error is similar to the one printed by Warn.
Examples: 
void test(T)()
{
    Checked!(int, Throw) x;
    x = 42;
    auto x1 = cast(T) x;
    writeln(x1); // 42
    x = T.max + 1;
    import std.exception : assertThrown, assertNotThrown;
    assertThrown(cast(T) x);
    x = x.max;
    assertThrown(x += 42);
    assertThrown(x += 42L);
    x = x.min;
    assertThrown(-x);
    assertThrown(x -= 42);
    assertThrown(x -= 42L);
    x = -1;
    assertNotThrown(x == -1);
    assertThrown(x == uint(-1));
    assertNotThrown(x <= -1);
    assertThrown(x <= uint(-1));
}
test!short;
test!(const short);
test!(immutable short);
class CheckFailure: object.Exception;
Exception type thrown upon any failure.
this(T...)(string f, T vals);
Parameters:
string f format specifier
T vals actual values for the format specifier
Dst onBadCast(Dst, Src)(Src src);
Called automatically upon a bad cast (one that loses precision or attempts to convert a negative value to an unsigned type). The source type is Src and the destination type is Dst.
Parameters:
Src src source operand
Returns:
Nominally the result is the desired value of the cast operation, which will be forwarded as the result of the cast. For Throw, the function never returns because it throws an exception.
Throws:
CheckFailure on bad cast
T onLowerBound(Rhs, T)(Rhs rhs, T bound);

T onUpperBound(Rhs, T)(Rhs rhs, T bound);
Called automatically upon a bounds error.
Parameters:
Rhs rhs The right-hand side value in the assignment, after the operator has been evaluated
T bound The value of the bound being violated
Returns:
Nominally the result is the desired value of the operator, which will be forwarded as result. For Throw, the function never returns because it throws.
Throws:
CheckFailure on overflow
bool hookOpEquals(L, R)(L lhs, R rhs);
Called automatically upon a comparison for equality. Throws upon an erroneous comparison (one that would make a signed negative value appear equal to an unsigned positive value).
Parameters:
L lhs The first argument of Checked, e.g. int if the left-hand side of the operator is Checked!int
R rhs The right-hand side type involved in the operator
Returns:
The result of the comparison.
Throws:
CheckFailure if the comparison is mathematically erroneous.
int hookOpCmp(Lhs, Rhs)(Lhs lhs, Rhs rhs);
Called automatically upon a comparison for ordering using one of the operators <, <=, >, or >=. In case the comparison is erroneous (i.e. it would make a signed negative value appear greater than or equal to an unsigned positive value), throws a Throw.CheckFailure exception. Otherwise, the three-state result is returned (positive if lhs > rhs, negative if lhs < rhs, 0 otherwise).
Parameters:
Lhs lhs The first argument of Checked, e.g. int if the left-hand side of the operator is Checked!int
Rhs rhs The right-hand side type involved in the operator
Returns:
For correct comparisons, returns a positive integer if lhs > rhs, a negative integer if lhs < rhs, 0 if the two are equal.
Throws:
Upon a mistaken comparison such as int(-1) < uint(0), the function never returns because it throws a Throw.CheckedFailure exception.
typeof(~Lhs()) onOverflow(string x, Lhs)(Lhs lhs);

typeof(Lhs() + Rhs()) onOverflow(string x, Lhs, Rhs)(Lhs lhs, Rhs rhs);
Called automatically upon an overflow during a unary or binary operation.
Parameters:
x The operator, e.g. -
Lhs lhs The left-hand side (or sole) argument
Rhs rhs The right-hand side type involved in the operator
Returns:
Nominally the result is the desired value of the operator, which will be forwarded as result. For Throw, the function never returns because it throws an exception.
Throws:
CheckFailure on overflow
struct Warn;
Hook that prints to stderr a trace of all integral errors, without affecting default behavior.
Examples: 
auto x = checked!Warn(42);
short x1 = cast(short) x;
//x += long(int.max);
auto y = checked!Warn(cast(const int) 42);
short y1 = cast(const byte) y;
Dst onBadCast(Dst, Src)(Src src);
Called automatically upon a bad cast from src to type Dst (one that loses precision or attempts to convert a negative value to an unsigned type).
Parameters:
Src src The source of the cast
Dst The target type of the cast
Returns:
cast(Dst) src
T onLowerBound(Rhs, T)(Rhs rhs, T bound);

T onUpperBound(Rhs, T)(Rhs rhs, T bound);
Called automatically upon a bad opOpAssign call (one that loses precision or attempts to convert a negative value to an unsigned type).
Parameters:
Rhs rhs The right-hand side value in the assignment, after the operator has been evaluated
T bound The bound being violated
Returns:
cast(T) rhs
bool hookOpEquals(Lhs, Rhs)(Lhs lhs, Rhs rhs);
Called automatically upon a comparison for equality. In case of an Erroneous comparison (one that would make a signed negative value appear equal to an unsigned positive value), writes a warning message to stderr as a side effect.
Parameters:
Lhs lhs The first argument of Checked, e.g. int if the left-hand side of the operator is Checked!int
Rhs rhs The right-hand side type involved in the operator
Returns:
In all cases the function returns the built-in result of lhs == rhs.
Examples: 
auto x = checked!Warn(-42);
// Passes
writeln(x); // -42
// Passes but prints a warning
// assert(x == uint(-42));
int hookOpCmp(Lhs, Rhs)(Lhs lhs, Rhs rhs);
Called automatically upon a comparison for ordering using one of the operators <, <=, >, or >=. In case the comparison is erroneous (i.e. it would make a signed negative value appear greater than or equal to an unsigned positive value), then a warning message is printed to stderr.
Parameters:
Lhs lhs The first argument of Checked, e.g. int if the left-hand side of the operator is Checked!int
Rhs rhs The right-hand side type involved in the operator
Returns:
In all cases, returns lhs < rhs ? -1 : lhs > rhs. The result is not autocorrected in case of an erroneous comparison.
Examples: 
auto x = checked!Warn(-42);
// Passes
assert(x <= -42);
// Passes but prints a warning
// assert(x <= uint(-42));
typeof(~Lhs()) onOverflow(string x, Lhs)(ref Lhs lhs);

typeof(Lhs() + Rhs()) onOverflow(string x, Lhs, Rhs)(Lhs lhs, Rhs rhs);
Called automatically upon an overflow during a unary or binary operation.
Parameters:
x The operator involved
Lhs The first argument of Checked, e.g. int if the left-hand side of the operator is Checked!int
Rhs The right-hand side type involved in the operator
Returns:
mixin(x ~ "lhs") for unary, mixin("lhs" ~ x ~ "rhs") for binary
struct ProperCompare;
Hook that provides arithmetically correct comparisons for equality and ordering. Comparing an object of type Checked!(X, ProperCompare) against another integral (for equality or ordering) ensures that no surprising conversions from signed to unsigned integral occur before the comparison. Using Checked!(X, ProperCompare) on either side of a comparison for equality against a floating-point number makes sure the integral can be properly converted to the floating point type, thus making sure equality is transitive.
Examples: 
alias opEqualsProper = ProperCompare.hookOpEquals;
assert(opEqualsProper(42, 42));
assert(opEqualsProper(42.0, 42.0));
assert(opEqualsProper(42u, 42));
assert(opEqualsProper(42, 42u));
writeln(-1); // 4294967295u
assert(!opEqualsProper(-1, 4294967295u));
assert(!opEqualsProper(const uint(-1), -1));
assert(!opEqualsProper(uint(-1), -1.0));
writeln(3_000_000_000U); // -1_294_967_296
assert(!opEqualsProper(3_000_000_000U, -1_294_967_296));
bool hookOpEquals(L, R)(L lhs, R rhs);
Hook for == and != that ensures comparison against integral values has the behavior expected by the usual arithmetic rules. The built-in semantics yield surprising behavior when comparing signed values against unsigned values for equality, for example uint.max == -1 or -1_294_967_296 == 3_000_000_000u. The call hookOpEquals(x, y) returns true if and only if x and y represent the same arithmetic number.
If one of the numbers is an integral and the other is a floating-point number, hookOpEquals(x, y) returns true if and only if the integral can be converted exactly (without approximation) to the floating-point number. This is in order to preserve transitivity of equality: if hookOpEquals(x, y) and hookOpEquals(y, z) then hookOpEquals(y, z), in case x, y, and z are a mix of integral and floating-point numbers.
Parameters:
L lhs The left-hand side of the comparison for equality
R rhs The right-hand side of the comparison for equality
Returns:
The result of the comparison, true if the values are equal
auto hookOpCmp(L, R)(L lhs, R rhs);
Hook for <, <=, >, and >= that ensures comparison against integral values has the behavior expected by the usual arithmetic rules. The built-in semantics yield surprising behavior when comparing signed values against unsigned values, for example 0u < -1. The call hookOpCmp(x, y) returns -1 if and only if x is smaller than y in abstract arithmetic sense.
If one of the numbers is an integral and the other is a floating-point number, hookOpEquals(x, y) returns a floating-point number that is -1 if x < y, 0 if x == y, 1 if x > y, and NaN if the floating-point number is NaN.
Parameters:
L lhs The left-hand side of the comparison for ordering
R rhs The right-hand side of the comparison for ordering
Returns:
The result of the comparison (negative if lhs < rhs, positive if lhs > rhs, 0 if the values are equal)
struct WithNaN;
Hook that reserves a special value as a "Not a Number" representative. For signed integrals, the reserved value is T.min. For signed integrals, the reserved value is T.max.
The default value of a Checked!(X, WithNaN) is its NaN value, so care must be taken that all variables are explicitly initialized. Any arithmetic and logic operation involving at least on NaN becomes NaN itself. All of a == b, a < b, a > b, a <= b, a >= b yield false if at least one of a and b is NaN.
Examples: 
auto x1 = Checked!(int, WithNaN)();
assert(x1.isNaN);
writeln(x1.get); // int.min
assert(x1 != x1);
assert(!(x1 < x1));
assert(!(x1 > x1));
assert(!(x1 == x1));
++x1;
assert(x1.isNaN);
writeln(x1.get); // int.min
--x1;
assert(x1.isNaN);
writeln(x1.get); // int.min
x1 = 42;
assert(!x1.isNaN);
writeln(x1); // x1
assert(x1 <= x1);
assert(x1 >= x1);
static assert(x1.min == int.min + 1);
x1 += long(int.max);
enum T defaultValue(T);
The default value used for values not explicitly initialized. It is the NaN value, i.e. T.min for signed integrals and T.max for unsigned integrals.
enum T max(T);

enum T min(T);
The maximum value representable is T.max for signed integrals, T.max - 1 for unsigned integrals. The minimum value representable is T.min + 1 for signed integrals, 0 for unsigned integrals.
Lhs hookOpCast(Lhs, Rhs)(Rhs rhs);
If rhs is WithNaN.defaultValue!Rhs, returns WithNaN.defaultValue!Lhs. Otherwise, returns cast(Lhs) rhs.
Parameters:
Rhs rhs the value being cast (Rhs is the first argument to Checked)
Lhs the target type of the cast
Returns:
The result of the cast operation.
Examples: 
auto x = checked!WithNaN(422);
writeln((cast(ubyte)x)); // 255
x = checked!WithNaN(-422);
writeln((cast(byte)x)); // -128
writeln(cast(short)x); // -422
assert(cast(bool) x);
x = x.init; // set back to NaN
assert(x != true);
assert(x != false);
bool hookOpEquals(Lhs, Rhs)(Lhs lhs, Rhs rhs);
Returns false if lhs == WithNaN.defaultValue!Lhs, lhs == rhs otherwise.
Parameters:
Lhs lhs The left-hand side of the comparison (Lhs is the first argument to Checked)
Rhs rhs The right-hand side of the comparison
Returns:
lhs != WithNaN.defaultValue!Lhs && lhs == rhs
double hookOpCmp(Lhs, Rhs)(Lhs lhs, Rhs rhs);
If lhs == WithNaN.defaultValue!Lhs, returns double.init. Otherwise, has the same semantics as the default comparison.
Parameters:
Lhs lhs The left-hand side of the comparison (Lhs is the first argument to Checked)
Rhs rhs The right-hand side of the comparison
Returns:
double.init if lhs == WitnNaN.defaultValue!Lhs, -1.0 if lhs < rhs, 0.0 if lhs == rhs, 1.0 if lhs > rhs.
Examples: 
Checked!(int, WithNaN) x;
assert(!(x < 0) && !(x > 0) && !(x == 0));
x = 1;
assert(x > 0 && !(x < 0) && !(x == 0));
auto hookOpUnary(string x, T)(ref T v);
Defines hooks for unary operators -, ~, ++, and --.
For - and ~, if v == WithNaN.defaultValue!T, returns WithNaN.defaultValue!T. Otherwise, the semantics is the same as for the built-in operator.
For ++ and --, if v == WithNaN.defaultValue!Lhs or the operation would result in an overflow, sets v to WithNaN.defaultValue!T. Otherwise, the semantics is the same as for the built-in operator.
Parameters:
x The operator symbol
T v The left-hand side of the comparison (T is the first argument to Checked)
Returns:
  • For x == "-" || x == "~": If v == WithNaN.defaultValue!T, the function returns WithNaN.defaultValue!T. Otherwise it returns the normal result of the operator.
  • For x == "++" || x == "--": The function returns void.
Examples: 
Checked!(int, WithNaN) x;
++x;
assert(x.isNaN);
x = 1;
assert(!x.isNaN);
x = -x;
++x;
assert(!x.isNaN);
auto hookOpBinary(string x, L, R)(L lhs, R rhs);
Defines hooks for binary operators +, -, *, /, %, ^^, &, |, ^, <<, >>, and >>> for cases where a Checked object is the left-hand side operand. If lhs == WithNaN.defaultValue!Lhs, returns WithNaN.defaultValue!(typeof(lhs + rhs)) without evaluating the operand. Otherwise, evaluates the operand. If evaluation does not overflow, returns the result. Otherwise, returns WithNaN.defaultValue!(typeof(lhs + rhs)).
Parameters:
x The operator symbol
L lhs The left-hand side operand (Lhs is the first argument to Checked)
R rhs The right-hand side operand
Returns:
If lhs != WithNaN.defaultValue!Lhs and the operator does not overflow, the function returns the same result as the built-in operator. In all other cases, returns WithNaN.defaultValue!(typeof(lhs + rhs)).
Examples: 
Checked!(int, WithNaN) x;
assert((x + 1).isNaN);
x = 100;
assert(!(x + 1).isNaN);
auto hookOpBinaryRight(string x, L, R)(L lhs, R rhs);
Defines hooks for binary operators +, -, *, /, %, ^^, &, |, ^, <<, >>, and >>> for cases where a Checked object is the right-hand side operand. If rhs == WithNaN.defaultValue!Rhs, returns WithNaN.defaultValue!(typeof(lhs + rhs)) without evaluating the operand. Otherwise, evaluates the operand. If evaluation does not overflow, returns the result. Otherwise, returns WithNaN.defaultValue!(typeof(lhs + rhs)).
Parameters:
x The operator symbol
L lhs The left-hand side operand
R rhs The right-hand side operand (Rhs is the first argument to Checked)
Returns:
If rhs != WithNaN.defaultValue!Rhs and the operator does not overflow, the function returns the same result as the built-in operator. In all other cases, returns WithNaN.defaultValue!(typeof(lhs + rhs)).
Examples: 
Checked!(int, WithNaN) x;
assert((1 + x).isNaN);
x = 100;
assert(!(1 + x).isNaN);
void hookOpOpAssign(string x, L, R)(ref L lhs, R rhs);
Defines hooks for binary operators +=, -=, *=, /=, %=, ^^=, &=, |=, ^=, <<=, >>=, and >>>= for cases where a Checked object is the left-hand side operand. If lhs == WithNaN.defaultValue!Lhs, no action is carried. Otherwise, evaluates the operand. If evaluation does not overflow and fits in Lhs without loss of information or change of sign, sets lhs to the result. Otherwise, sets lhs to WithNaN.defaultValue!Lhs.
Parameters:
x The operator symbol (without the =)
L lhs The left-hand side operand (Lhs is the first argument to Checked)
R rhs The right-hand side operand
Returns:
void
Examples: 
Checked!(int, WithNaN) x;
x += 4;
assert(x.isNaN);
x = 0;
x += 4;
assert(!x.isNaN);
x += int.max;
assert(x.isNaN);
bool isNaN(T)(const Checked!(T, WithNaN) x);
Queries whether a Checked!(T, WithNaN) object is not a number (NaN).
Parameters:
Checked!(T, WithNaN) x the Checked instance queried
Returns:
true if x is a NaN, false otherwise
Examples: 
auto x1 = Checked!(int, WithNaN)();
assert(x1.isNaN);
x1 = 1;
assert(!x1.isNaN);
x1 = x1.init;
assert(x1.isNaN);
struct Saturate;
Hook that implements saturation, i.e. any arithmetic operation that would overflow leaves the result at its extreme value (min or max depending on the direction of the overflow).
Saturation is not sticky; if a value reaches its saturation value, another operation may take it back to normal range.
Examples: 
auto x = checked!Saturate(int.max);
++x;
writeln(x); // int.max
--x;
writeln(x); // int.max - 1
x = int.min;
writeln(-x); // int.max
x -= 42;
writeln(x); // int.min
writeln(x * -2); // int.max
T onLowerBound(Rhs, T)(Rhs, T bound);

T onUpperBound(Rhs, T)(Rhs, T bound);
Implements saturation for operators +=, -=, *=, /=, %=, ^^=, &=, |=, ^=, <<=, >>=, and >>>=. This hook is called if the result of the binary operation does not fit in Lhs without loss of information or a change in sign.
Parameters:
Rhs The right-hand side type in the assignment, after the operation has been computed
T bound The bound being violated
Returns:
Lhs.max if rhs >= 0, Lhs.min otherwise.
Examples: 
auto x = checked!Saturate(short(100));
x += 33000;
writeln(x); // short.max
x -= 70000;
writeln(x); // short.min
auto onOverflow(string x, Lhs)(Lhs);

typeof(Lhs() + Rhs()) onOverflow(string x, Lhs, Rhs)(Lhs lhs, Rhs rhs);
Implements saturation for operators +, - (unary and binary), *, /, %, ^^, &, |, ^, <<, >>, and >>>.
For unary -, onOverflow is called if lhs == Lhs.min and Lhs is a signed type. The function returns Lhs.max.
For binary operators, the result is as follows:
  • Lhs.max if the result overflows in the positive direction, on division by 0, or on shifting right by a negative value
  • Lhs.min if the result overflows in the negative direction
  • 0 if lhs is being shifted left by a negative value, or shifted right by a large positive value
Parameters:
x The operator involved in the opAssign operation
Lhs The left-hand side type of the operator (Lhs is the first argument to Checked)
Rhs The right-hand side type in the operator
Returns:
The saturated result of the operator.
Examples: 
writeln(checked!Saturate(int.max) + 1); // int.max
writeln(checked!Saturate(100)^^10); // int.max
writeln(checked!Saturate(-100)^^10); // int.max
writeln(checked!Saturate(100) / 0); // int.max
writeln(checked!Saturate(100) << -1); // 0
writeln(checked!Saturate(100) << 33); // int.max
writeln(checked!Saturate(100) >> -1); // int.max
writeln(checked!Saturate(100) >> 33); // 0
typeof(mixin(x == "cmp" ? "0" : "L() " ~ x ~ " R()")) opChecked(string x, L, R)(const L lhs, const R rhs, ref bool overflow)
if (isIntegral!L && isIntegral!R);
Defines binary operations with overflow checking for any two integral types. The result type obeys the language rules (even when they may be counterintuitive), and overflow is set if an overflow occurs (including inadvertent change of signedness, e.g. -1 is converted to uint). Conceptually the behavior is:
  1. Perform the operation in infinite precision
  2. If the infinite-precision result fits in the result type, return it and do not touch overflow
  3. Otherwise, set overflow to true and return an unspecified value
The implementation exploits properties of types and operations to minimize additional work.
Parameters:
x The binary operator involved, e.g. /
L lhs The left-hand side of the operator
R rhs The right-hand side of the operator
bool overflow The overflow indicator (assigned true in case there's an error)
Returns:
The result of the operation, which is the same as the built-in operator
Examples: 
bool overflow;
assert(opChecked!"+"(const short(1), short(1), overflow) == 2 && !overflow);
assert(opChecked!"+"(1, 1, overflow) == 2 && !overflow);
assert(opChecked!"+"(1, 1u, overflow) == 2 && !overflow);
assert(opChecked!"+"(-1, 1u, overflow) == 0 && !overflow);
assert(opChecked!"+"(1u, -1, overflow) == 0 && !overflow);
Examples: 
bool overflow;
assert(opChecked!"-"(1, 1, overflow) == 0 && !overflow);
assert(opChecked!"-"(1, 1u, overflow) == 0 && !overflow);
assert(opChecked!"-"(1u, -1, overflow) == 2 && !overflow);
assert(opChecked!"-"(-1, 1u, overflow) == 0 && overflow);