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Function std.checkedint.opChecked

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:

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);

  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.


x The binary operator involved, e.g. /
lhs The left-hand side of the operator
rhs The right-hand side of the operator
overflow The overflow indicator (assigned true in case there's an error)


The result of the operation, which is the same as the built-in operator


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);


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);


struct MyHook
    static size_t hookToHash(T)(const T payload) nothrow @trusted
        return .hashOf(payload);

int[Checked!(int, MyHook)] aa;
Checked!(int, MyHook) var = 42;
aa[var] = 100;

writeln(aa[var]); // 100

int[Checked!(int, Abort)] bb;
Checked!(int, Abort) var2 = 42;
bb[var2] = 100;

writeln(bb[var2]); // 100