CODEWITHSUNDEEP
c++lambdatype-traits
Tareq A. Siraj
Tareq A. Siraj

Reputation: 424

Are lambda functions nothrow_move_assignable?

clang-cl (4.0.0-trunk) seems to think yes while vc2015 (update3) thinks no.

Is this implementation defined or the standard dictates how lambda functions should be implemented in terms or nothrow and move assignable?

#include <type_traits>
#include <iostream>

template <typename T>
void test_nothrow_move_assignable(T&&) {
  std::cout << std::boolalpha
    << std::is_nothrow_move_assignable<T>::value
    << "\n";
}

int main() {
  test_nothrow_move_assignable([]{});
  return 0;
}

// $ clang-cl.exe scratch.cpp
// $ scratch.exe
// true

// $ cl /nologo /EHsc scratch.cpp
// scratch.cpp
// $ scratch.exe
// false

Upvotes: 4

Views: 212

Answers (1)

Barry
Barry

Reputation: 303147

This is clang bug. From [expr.prim.lambda]:

The closure type associated with a lambda-expression has no default constructor and a deleted copy assignment operator. It has a defaulted copy constructor and a defaulted move constructor (12.8).

So the type shouldn't be move assignable at all, much less nothrow move assignable.

Upvotes: 4

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