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std.exception
This module defines functions related to exceptions and general error
handling. It also defines functions intended to aid in unit testing.
Category | Functions |
---|---|
Assumptions | assertNotThrown assertThrown assumeUnique assumeWontThrow mayPointTo |
Enforce | doesPointTo enforce errnoEnforce |
Handlers | collectException collectExceptionMsg ifThrown handle |
Other | basicExceptionCtors emptyExceptionMsg ErrnoException RangePrimitive |
License:
Authors:
Source std/exception.d
Examples:
Synopis
import core.stdc.stdlib : malloc, free; import std.algorithm.comparison : equal; import std.algorithm.iteration : map, splitter; import std.algorithm.searching : endsWith; import std.conv : ConvException, to; import std.range : front, retro; // use enforce like assert int a = 3; enforce(a > 2, "a needs to be higher than 2."); // enforce can throw a custom exception enforce!ConvException(a > 2, "a needs to be higher than 2."); // enforce will return it's input enum size = 42; auto memory = enforce(malloc(size), "malloc failed")[0 .. size]; scope(exit) free(memory.ptr); // collectException can be used to test for exceptions Exception e = collectException("abc".to!int); assert(e.file.endsWith("conv.d")); // and just for the exception message string msg = collectExceptionMsg("abc".to!int); writeln(msg); // "Unexpected 'a' when converting from type string to type int" // assertThrown can be used to assert that an exception is thrown assertThrown!ConvException("abc".to!int); // ifThrown can be used to provide a default value if an exception is thrown writeln("x".to!int().ifThrown(0)); // 0 // handle is a more advanced version of ifThrown for ranges auto r = "12,1337z32,54".splitter(',').map!(a => to!int(a)); auto h = r.handle!(ConvException, RangePrimitive.front, (e, r) => 0); assert(h.equal([12, 0, 54])); assertThrown!ConvException(h.retro.equal([54, 0, 12])); // basicExceptionCtors avoids the boilerplate when creating custom exceptions static class MeaCulpa : Exception { mixin basicExceptionCtors; } e = collectException((){throw new MeaCulpa("diagnostic message");}()); writeln(e.msg); // "diagnostic message" writeln(e.file); // __FILE__ writeln(e.line); // __LINE__ - 3 // assumeWontThrow can be used to cast throwing code into `nothrow` void exceptionFreeCode() nothrow { // auto-decoding only throws if an invalid UTF char is given assumeWontThrow("abc".front); } // assumeUnique can be used to cast mutable instance to an `immutable` one // use with care char[] str = " mutable".dup; str[0 .. 2] = "im"; immutable res = assumeUnique(str); writeln(res); // "immutable"
- auto
assertNotThrown
(T : Throwable = Exception, E)(lazy Eexpression
, stringmsg
= null, stringfile
= __FILE__, size_tline
= __LINE__); - Asserts that the given expression does not throw the given type of Throwable. If a Throwable of the given type is thrown, it is caught and does not escape assertNotThrown. Rather, an AssertError is thrown. However, any other Throwables will escape.Parameters:
T The Throwable to test for. E expression
The expression to test. string msg
Optional message to output on test failure. If msg is empty, and the thrown exception has a non-empty msg field, the exception's msg field will be output on test failure. string file
The file where the error occurred. Defaults to __FILE__. size_t line
The line where the error occurred. Defaults to __LINE__. Throws:AssertError if the given Throwable is thrown.Returns:the result ofexpression
.Examples:import core.exception : AssertError; import std.string; assertNotThrown!StringException(enforce!StringException(true, "Error!")); //Exception is the default. assertNotThrown(enforce!StringException(true, "Error!")); assert(collectExceptionMsg!AssertError(assertNotThrown!StringException( enforce!StringException(false, "Error!"))) == `assertNotThrown failed: StringException was thrown: Error!`);
- void
assertThrown
(T : Throwable = Exception, E)(lazy Eexpression
, stringmsg
= null, stringfile
= __FILE__, size_tline
= __LINE__); - Asserts that the given expression throws the given type of Throwable. The Throwable is caught and does not escape assertThrown. However, any other Throwables will escape, and if no Throwable of the given type is thrown, then an AssertError is thrown.Parameters:
T The Throwable to test for. E expression
The expression to test. string msg
Optional message to output on test failure. string file
The file where the error occurred. Defaults to __FILE__. size_t line
The line where the error occurred. Defaults to __LINE__. Throws:AssertError if the given Throwable is not thrown.Examples:import core.exception : AssertError; import std.string; assertThrown!StringException(enforce!StringException(false, "Error!")); //Exception is the default. assertThrown(enforce!StringException(false, "Error!")); assert(collectExceptionMsg!AssertError(assertThrown!StringException( enforce!StringException(true, "Error!"))) == `assertThrown failed: No StringException was thrown.`);
- template
enforce
(E : Throwable = Exception) if (is(typeof(new E("", string.init, size_t.init)) : Throwable) || is(typeof(new E(string.init, size_t.init)) : Throwable))
Tenforce
(T, Dg, string file = __FILE__, size_t line = __LINE__)(Tvalue
, scope Dgdg
)
if (isSomeFunction!Dg && is(typeof(dg
())) && is(typeof(() { if (!value
) { } } )));
Tenforce
(T)(Tvalue
, lazy Throwableex
); - Enforces that the given value is true. If the given value is false, an exception is thrown. The
- msg - error message as a string
dg
- custom delegate that return a string and is only called if an exception occurredex
- custom exception to be thrown. It is lazy and is only created if an exception occurred
Parameters:T value
The value to test. E Exception type to throw if the value evaluates to false. const(char)[] msg The error message to put in the exception if it is thrown. Dg dg
The delegate to be called if the value evaluates to false. Throwable ex
The exception to throw if the value evaluates to false. string file The source file of the caller. size_t line The line number of the caller. Returns:value
, if cast(bool)value
is true. Otherwise, depending on the chosen overload, new Exception(msg),dg
() orex
is thrown.Note:Do not useenforce
is used to throw exceptions and is therefore intended to aid in error handling. It is not intended for verifying the logic of your program - that is what assert is for.enforce
inside of contracts (i.e. inside of in and out blocks and invariants), because contracts are compiled out when compiling with -release.Examples:import core.stdc.stdlib : malloc, free; import std.conv : ConvException, to; // use enforce like assert int a = 3; enforce(a > 2, "a needs to be higher than 2."); // enforce can throw a custom exception enforce!ConvException(a > 2, "a needs to be higher than 2."); // enforce will return it's input enum size = 42; auto memory = enforce(malloc(size), "malloc failed")[0 .. size]; scope(exit) free(memory.ptr);
Examples:assertNotThrown(enforce(true, new Exception("this should not be thrown"))); assertThrown(enforce(false, new Exception("this should be thrown")));
Examples:writeln(enforce(123)); // 123 try { enforce(false, "error"); assert(false); } catch (Exception e) { writeln(e.msg); // "error" writeln(e.file); // __FILE__ writeln(e.line); // __LINE__ - 7 }
Examples:Alias your own enforce functionimport std.conv : ConvException; alias convEnforce = enforce!ConvException; assertNotThrown(convEnforce(true)); assertThrown!ConvException(convEnforce(false, "blah"));
- T
enforce
(T)(Tvalue
, lazy const(char)[]msg
= null, stringfile
= __FILE__, size_tline
= __LINE__)
if (is(typeof(() { if (!value
) { } } )));
- alias
errnoEnforce
= enforce!(ErrnoException).enforce(T)(T value, lazy const(char)[] msg = null, string file = __FILE__, size_t line = __LINE__) if (is(typeof(() { if (!value) { } } ))); - Enforces that the given value is true, throwing an ErrnoException if it is not.Parameters:
T value The value to test. const(char)[] msg The message to include in the ErrnoException if it is thrown. Returns:value, if cast(bool) value is true. Otherwise, new ErrnoException(msg) is thrown. It is assumed that the last operation set errno to an error code corresponding with the failed condition.Examples:import core.stdc.stdio : fclose, fgets, fopen; import std.file : thisExePath; import std.string : toStringz; auto f = fopen(thisExePath.toStringz, "r").errnoEnforce; scope(exit) fclose(f); char[100] buf; auto line = fgets(buf.ptr, buf.length, f); enforce(line !is null); // expect a non-empty line
- T
collectException
(T = Exception, E)(lazy Eexpression
, ref Eresult
); - Catches and returns the exception thrown from the given expression. If no exception is thrown, then null is returned and
result
is set to the result of the expression.Note that whilecollectException
can be used to collect any Throwable and not just Exceptions, it is generally ill-advised to catch anything that is neither an Exception nor a type derived from Exception. So, do not usecollectException
to collect non-Exceptions unless you're sure that that's what you really want to do.Parameters:T The type of exception to catch. E expression
The expression which may throw an exception. E result
The result of the expression if no exception is thrown. Examples:int b; int foo() { throw new Exception("blah"); } assert(collectException(foo(), b)); version (D_NoBoundsChecks) {} else { // check for out of bounds error int[] a = new int[3]; import core.exception : RangeError; assert(collectException!RangeError(a[4], b)); }
- T
collectException
(T : Throwable = Exception, E)(lazy Eexpression
); - Catches and returns the exception thrown from the given expression. If no exception is thrown, then null is returned. E can be void.Note that while
collectException
can be used to collect any Throwable and not just Exceptions, it is generally ill-advised to catch anything that is neither an Exception nor a type derived from Exception. So, do not usecollectException
to collect non-Exceptions unless you're sure that that's what you really want to do.Parameters:T The type of exception to catch. E expression
The expression which may throw an exception. Examples:int foo() { throw new Exception("blah"); } writeln(collectException(foo()).msg); // "blah"
- string
collectExceptionMsg
(T = Exception, E)(lazy Eexpression
); - Catches the exception thrown from the given expression and returns the msg property of that exception. If no exception is thrown, then null is returned. E can be void.If an exception is thrown but it has an empty message, then emptyExceptionMsg is returned. Note that while
collectExceptionMsg
can be used to collect any Throwable and not just Exceptions, it is generally ill-advised to catch anything that is neither an Exception nor a type derived from Exception. So, do not usecollectExceptionMsg
to collect non-Exceptions unless you're sure that that's what you really want to do.Parameters:T The type of exception to catch. E expression
The expression which may throw an exception. Examples:void throwFunc() { throw new Exception("My Message."); } writeln(collectExceptionMsg(throwFunc())); // "My Message." void nothrowFunc() {} assert(collectExceptionMsg(nothrowFunc()) is null); void throwEmptyFunc() { throw new Exception(""); } writeln(collectExceptionMsg(throwEmptyFunc())); // emptyExceptionMsg
- enum string
emptyExceptionMsg
; - Value that collectExceptionMsg returns when it catches an exception with an empty exception message.
- pure nothrow immutable(T)[]
assumeUnique
(T)(T[]array
);
pure nothrow immutable(T)[]assumeUnique
(T)(ref T[]array
);
pure nothrow immutable(T[U])assumeUnique
(T, U)(ref T[U]array
); - Casts a mutable array to an immutable array in an idiomatic manner. Technically,
assumeUnique
just inserts a cast, but its name documents assumptions on the part of the caller.assumeUnique
(arr) should only be called when there are no more active mutable aliases to elements of arr. To strengthen this assumption,assumeUnique
(arr) also clears arr before returning. Essentially assumeUnique(arr) indicates commitment from the caller that there is no more mutable access to any of arr's elements (transitively), and that all future accesses will be done through the immutable array returned byassumeUnique
.Typically,assumeUnique
is used to return arrays from functions that have allocated and built them.Parameters:T[] array
The array to cast to immutable. Returns:The immutable array.Example
string letters() { char[] result = new char['z' - 'a' + 1]; foreach (i, ref e; result) { e = cast(char)('a' + i); } return assumeUnique(result); }
assumeUnique
.Bad
char[] buffer; string letters(char first, char last) { if (first >= last) return null; // fine auto sneaky = buffer; sneaky.length = last - first + 1; foreach (i, ref e; sneaky) { e = cast(char)('a' + i); } return assumeUnique(sneaky); // BAD }
return to!(string)(sneaky); // not that sneaky anymore
The to call will duplicate the array appropriately.The downside of usingNote: Checking for uniqueness during compilation is possible in certain cases, especially when a function is marked (or inferred) as pure. The following example does not need to callassumeUnique
because the compiler can infer the uniqueness of the array in the pure function:static string letters() pure { char[] result = new char['z' - 'a' + 1]; foreach (i, ref e; result) { e = cast(char)('a' + i); } return result; }
assumeUnique
's convention-based usage is that at this time there is no formal checking of the correctness of the assumption; on the upside, the idiomatic use ofassumeUnique
is simple and rare enough to be tolerable.Examples:int[] arr = new int[1]; auto arr1 = arr.assumeUnique; static assert(is(typeof(arr1) == immutable(int)[])); writeln(arr); // null writeln(arr1); // [0]
Examples:int[string] arr = ["a":1]; auto arr1 = arr.assumeUnique; static assert(is(typeof(arr1) == immutable(int[string]))); writeln(arr); // null writeln(arr1.keys); // ["a"]
- nothrow T
assumeWontThrow
(T)(lazy Texpr
, stringmsg
= null, stringfile
= __FILE__, size_tline
= __LINE__); - Wraps a possibly-throwing expression in a nothrow wrapper so that it can be called by a nothrow function.This wrapper function documents commitment on the part of the caller that the appropriate steps have been taken to avoid whatever conditions may trigger an exception during the evaluation of
expr
. If it turns out that the expression does throw at runtime, the wrapper will throw an AssertError. (Note that Throwable objects such as AssertError that do not subclass Exception may be thrown even from nothrow functions, since they are considered to be serious runtime problems that cannot be recovered from.)Parameters:T expr
The expression asserted not to throw. string msg
The message to include in the AssertError if the assumption turns out to be false. string file
The source file name of the caller. size_t line
The line number of the caller. Returns:The value ofexpr
, if any.Examples:import std.math.algebraic : sqrt; // This function may throw. int squareRoot(int x) { if (x < 0) throw new Exception("Tried to take root of negative number"); return cast(int) sqrt(cast(double) x); } // This function never throws. int computeLength(int x, int y) nothrow { // Since x*x + y*y is always positive, we can safely assume squareRoot // won't throw, and use it to implement this nothrow function. If it // does throw (e.g., if x*x + y*y overflows a 32-bit value), then the // program will terminate. return assumeWontThrow(squareRoot(x*x + y*y)); } writeln(computeLength(3, 4)); // 5
- pure nothrow @nogc @trusted bool
doesPointTo
(S, T, Tdummy = void)(auto const ref Ssource
, const ref Ttarget
)
if (__traits(isRef,source
) || isDynamicArray!S || is(S == U*, U) || is(S == class));
pure nothrow @trusted booldoesPointTo
(S, T)(auto const shared ref Ssource
, const shared ref Ttarget
);
pure nothrow @trusted boolmayPointTo
(S, T, Tdummy = void)(auto const ref Ssource
, const ref Ttarget
)
if (__traits(isRef,source
) || isDynamicArray!S || is(S == U*, U) || is(S == class));
pure nothrow @trusted boolmayPointTo
(S, T)(auto const shared ref Ssource
, const shared ref Ttarget
); - Checks whether a given source object contains pointers or references to a given target object.Parameters:
S source
The source object T target
The target object Bugs:The function is explicitly annotated @nogc because inference could fail, see Bugzilla issue 17084.Returns:true ifsource
's representation embeds a pointer that points totarget
's representation or somewhere inside it. Ifsource
is or contains a dynamic array, then, then these functions will check if there is overlap between the dynamic array andtarget
's representation. Ifsource
is a class, then it will be handled as a pointer. Iftarget
is a pointer, a dynamic array or a class, then these functions will only check ifsource
points totarget
, not whattarget
references. Ifsource
is or contains a union or void[n], then there may be either false positives or false negatives:doesPointTo
will return true if it is absolutely certainsource
points totarget
. It may produce false negatives, but never false positives. This function should be prefered when trying to validate input data.mayPointTo
will return false if it is absolutely certainsource
does not point totarget
. It may produce false positives, but never false negatives. This function should be prefered for defensively choosing a code path.Note Evaluating doesPointTo(x, x) checks whether x has internal pointers. This should only be done as an assertive test, as the language is free to assume objects don't have internal pointers (TDPL 7.1.3.5).
Examples:Pointersint i = 0; int* p = null; assert(!p.doesPointTo(i)); p = &i; assert( p.doesPointTo(i));
Examples:Structs and Unionsstruct S { int v; int* p; } int i; auto s = S(0, &i); // structs and unions "own" their members // pointsTo will answer true if one of the members pointsTo. assert(!s.doesPointTo(s.v)); //s.v is just v member of s, so not pointed. assert( s.p.doesPointTo(i)); //i is pointed by s.p. assert( s .doesPointTo(i)); //which means i is pointed by s itself. // Unions will behave exactly the same. Points to will check each "member" // individually, even if they share the same memory
Examples:Arrays (dynamic and static)int i; // trick the compiler when initializing slice // https://issues.dlang.org/show_bug.cgi?id=18637 int* p = &i; int[] slice = [0, 1, 2, 3, 4]; int[5] arr = [0, 1, 2, 3, 4]; int*[] slicep = [p]; int*[1] arrp = [&i]; // A slice points to all of its members: assert( slice.doesPointTo(slice[3])); assert(!slice[0 .. 2].doesPointTo(slice[3])); // Object 3 is outside of the // slice [0 .. 2] // Note that a slice will not take into account what its members point to. assert( slicep[0].doesPointTo(i)); assert(!slicep .doesPointTo(i)); // static arrays are objects that own their members, just like structs: assert(!arr.doesPointTo(arr[0])); // arr[0] is just a member of arr, so not // pointed. assert( arrp[0].doesPointTo(i)); // i is pointed by arrp[0]. assert( arrp .doesPointTo(i)); // which means i is pointed by arrp // itself. // Notice the difference between static and dynamic arrays: assert(!arr .doesPointTo(arr[0])); assert( arr[].doesPointTo(arr[0])); assert( arrp .doesPointTo(i)); assert(!arrp[].doesPointTo(i));
Examples:Classesclass C { this(int* p){this.p = p;} int* p; } int i; C a = new C(&i); C b = a; // Classes are a bit particular, as they are treated like simple pointers // to a class payload. assert( a.p.doesPointTo(i)); // a.p points to i. assert(!a .doesPointTo(i)); // Yet a itself does not point i. //To check the class payload itself, iterate on its members: () { import std.traits : Fields; foreach (index, _; Fields!C) if (doesPointTo(a.tupleof[index], i)) return; assert(0); }(); // To check if a class points a specific payload, a direct memmory check // can be done: auto aLoc = cast(ubyte[__traits(classInstanceSize, C)]*) a; assert(b.doesPointTo(*aLoc)); // b points to where a is pointing
- class
ErrnoException
: object.Exception; - Thrown if errors that set errno occur.Examples:
import core.stdc.errno : EAGAIN; auto ex = new ErrnoException("oh no", EAGAIN); writeln(ex.errno); // EAGAIN
Examples:errno is used by default if no explicit error code is providedimport core.stdc.errno : errno, EAGAIN; auto old = errno; scope(exit) errno = old; // fake that errno got set by the callee errno = EAGAIN; auto ex = new ErrnoException("oh no"); writeln(ex.errno); // EAGAIN
- final pure nothrow @nogc @property scope @safe uint
errno
(); - Operating system error code.
- final pure nothrow @nogc @property scope @safe string
errnoMsg
(); - Localized error message generated through core.stdc.string.strerror_r or core.stdc.string.strerror.
- @safe this(string
msg
, stringfile
= null, size_tline
= 0); - Constructor which takes an error message. The current global core.stdc.errno.errno value is used as error code.
- @safe this(string
msg
, interrno
, stringfile
= null, size_tline
= 0); - Constructor which takes an error message and error code.
- CommonType!(T1, T2)
ifThrown
(E : Throwable = Exception, T1, T2)(lazy scope T1expression
, lazy scope T2errorHandler
);
CommonType!(T1, T2)ifThrown
(E : Throwable, T1, T2)(lazy scope T1expression
, scope T2 delegate(E)errorHandler
);
CommonType!(T1, T2)ifThrown
(T1, T2)(lazy scope T1expression
, scope T2 delegate(Exception)errorHandler
); - ML-style functional exception handling. Runs the supplied expression and returns its result. If the expression throws a Throwable, runs the supplied error handler instead and return its result. The error handler's type must be the same as the expression's type.Parameters:
E The type of Throwables to catch. Defaults to Exception T1 The type of the expression. T2 The return type of the error handler. T1 expression
The expression to run and return its result. T2 errorHandler
The handler to run if the expression throwed. Returns:expression, if it does not throw. Otherwise, returns the result of errorHandler.Examples:Revert to a default value upon an error:import std.conv : to; writeln("x".to!int.ifThrown(0)); // 0
Examples:Chain multiple calls to ifThrown, each capturing errors from the entire preceding expression.import std.conv : ConvException, to; string s = "true"; assert(s.to!int.ifThrown(cast(int) s.to!double) .ifThrown(cast(int) s.to!bool) == 1); s = "2.0"; assert(s.to!int.ifThrown(cast(int) s.to!double) .ifThrown(cast(int) s.to!bool) == 2); // Respond differently to different types of errors alias orFallback = (lazy a) => a.ifThrown!ConvException("not a number") .ifThrown!Exception("number too small"); writeln(orFallback(enforce("x".to!int < 1).to!string)); // "not a number" writeln(orFallback(enforce("2".to!int < 1).to!string)); // "number too small"
Examples:The expression and the errorHandler must have a common type they can both be implicitly casted to, and that type will be the type of the compound expression.// null and new Object have a common type(Object). static assert(is(typeof(null.ifThrown(new Object())) == Object)); static assert(is(typeof((new Object()).ifThrown(null)) == Object)); // 1 and new Object do not have a common type. static assert(!__traits(compiles, 1.ifThrown(new Object()))); static assert(!__traits(compiles, (new Object()).ifThrown(1)));
Examples:Use a lambda to get the thrown object.import std.format : format; // "std.format.FormatException" writeln("%s".format.ifThrown!Exception(e => e.classinfo.name));
- enum
RangePrimitive
: int; - This enum is used to select the primitives of the range to handle by the handle range wrapper. The values of the enum can be OR'd to select multiple primitives to be handled.
RangePrimitive
.access is a shortcut for the access primitives; front, back and opIndex.RangePrimitive
.pop is a shortcut for the mutating primitives; popFront and popBack.Examples:import std.algorithm.comparison : equal; import std.algorithm.iteration : map, splitter; import std.conv : to, ConvException; auto s = "12,1337z32,54,2,7,9,1z,6,8"; // The next line composition will throw when iterated // as some elements of the input do not convert to integer auto r = s.splitter(',').map!(a => to!int(a)); // Substitute 0 for cases of ConvException auto h = r.handle!(ConvException, RangePrimitive.front, (e, r) => 0); assert(h.equal([12, 0, 54, 2, 7, 9, 0, 6, 8]));
Examples:import std.algorithm.comparison : equal; import std.range : retro; import std.utf : UTFException; auto str = "hello\xFFworld"; // 0xFF is an invalid UTF-8 code unit auto handled = str.handle!(UTFException, RangePrimitive.access, (e, r) => ' '); // Replace invalid code points with spaces assert(handled.equal("hello world")); // `front` is handled, assert(handled.retro.equal("dlrow olleh")); // as well as `back`
front
back
popFront
popBack
empty
save
length
opDollar
opIndex
opSlice
access
pop
- auto
handle
(E : Throwable, RangePrimitive primitivesToHandle, alias handler, Range)(Rangeinput
)
if (isInputRange!Range); - Handle exceptions thrown from range primitives.Use the RangePrimitive enum to specify which primitives to handle. Multiple range primitives can be handled at once by using the OR operator or the pseudo-primitives RangePrimitive.access and RangePrimitive.pop. All handled primitives must have return types or values compatible with the user-supplied handler.Parameters:
E The type of Throwable to handle. primitivesToHandle Set of range primitives to handle. handler The callable that is called when a handled primitive throws a Throwable of type E. The handler must accept arguments of the form E, ref IRange and its return value is used as the primitive's return value whenever E is thrown. For opIndex, the handler can optionally recieve a third argument; the index that caused the exception. Range input
The range to handle. Returns:A wrapper struct that preserves the range interface ofinput
.Note Infinite ranges with slicing support must return an instance of std.range.Take when sliced with a specific lower and upper bound (see std.range.primitives.hasSlicing);
handle
deals with this by takeing 0 from the return value of the handler function and returning that when an exception is caught.Examples:import std.algorithm.comparison : equal; import std.algorithm.iteration : map, splitter; import std.conv : to, ConvException; auto s = "12,1337z32,54,2,7,9,1z,6,8"; // The next line composition will throw when iterated // as some elements of the input do not convert to integer auto r = s.splitter(',').map!(a => to!int(a)); // Substitute 0 for cases of ConvException auto h = r.handle!(ConvException, RangePrimitive.front, (e, r) => 0); assert(h.equal([12, 0, 54, 2, 7, 9, 0, 6, 8]));
Examples:import std.algorithm.comparison : equal; import std.range : retro; import std.utf : UTFException; auto str = "hello\xFFworld"; // 0xFF is an invalid UTF-8 code unit auto handled = str.handle!(UTFException, RangePrimitive.access, (e, r) => ' '); // Replace invalid code points with spaces assert(handled.equal("hello world")); // `front` is handled, assert(handled.retro.equal("dlrow olleh")); // as well as `back`
- template
basicExceptionCtors
() - Convenience mixin for trivially sub-classing exceptionsEven trivially sub-classing an exception involves writing boilerplate code for the constructor to: 1) correctly pass in the source file and line number the exception was thrown from; 2) be usable with enforce which expects exception constructors to take arguments in a fixed order. This mixin provides that boilerplate code. Note however that you need to mark the mixin line with at least a minimal (i.e. just ///) DDoc comment if you want the mixed-in constructors to be documented in the newly created Exception subclass. Current limitation: Due to bug #11500, currently the constructors specified in this mixin cannot be overloaded with any other custom constructors. Thus this mixin can currently only be used when no such custom constructors need to be explicitly specified.Examples:
class MeaCulpa: Exception { /// mixin basicExceptionCtors; } try throw new MeaCulpa("test"); catch (MeaCulpa e) { writeln(e.msg); // "test" writeln(e.file); // __FILE__ writeln(e.line); // __LINE__ - 5 }
- pure nothrow @nogc @safe this(string
msg
, stringfile
= __FILE__, size_tline
= __LINE__, Throwablenext
= null); - Parameters:
string msg
The message for the exception. string file
The file where the exception occurred. size_t line
The line number where the exception occurred. Throwable next
The previous exception in the chain of exceptions, if any. - pure nothrow @nogc @safe this(string
msg
, Throwablenext
, stringfile
= __FILE__, size_tline
= __LINE__); - Parameters:
string msg
The message for the exception. Throwable next
The previous exception in the chain of exceptions. string file
The file where the exception occurred. size_t line
The line number where the exception occurred.
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