Viewing file:  constexpr-lambda6.C (1.01 KB) -rw-r--r--
Select action/file-type:
 (+) |  (+) |  (+) | Code (+) | Session (+) |  (+) | SDB (+) |  (+) |  (+) |  (+) |  (+) |  (+) |
// Testcase from P0170R1
// { dg-do compile { target c++17 } }
auto monoid = [](auto v) { return [=] { return v; }; };
auto add = [](auto m1) constexpr {
auto ret = m1();
return [=](auto m2) mutable {
auto m1val = m1();
auto plus = [=] (auto m2val) mutable constexpr
{ return m1val += m2val; };
ret = plus(m2());
return monoid(ret);
};
};
int main()
{
constexpr auto zero = monoid(0);
constexpr auto one = monoid(1);
static_assert(add(one)(zero)() == one()); // OK
// Since 'two' below is not declared constexpr, an evaluation of its constexpr
// member function call operator can not perform an lvalue-to-rvalue conversion
// on one of its subobjects (that represents its capture) in a constant
// expression.
auto two = monoid(2);
if (!(two() == 2)) __builtin_abort(); // OK, not a constant expression.
static_assert(add(one)(one)() == two()); // { dg-error "|in .constexpr. expansion of " } two() is not a constant expression
static_assert(add(one)(one)() == monoid(2)()); // OK
}
|
