Re: [PATCH 1/2] PR c++/61636

[Adam Butcher <adam@jessamine.co.uk>]

On 2015-04-17 22:06, Adam Butcher wrote:
> On 2015-04-17 20:58, Jason Merrill wrote:
>> On 04/09/2015 11:31 PM, Adam Butcher wrote:
>>> +		/* For generic lambdas, resolve default captured 'this' now.  */
>>>
>> This isn't quite right.  We don't want to capture 'this' any time we
>> see a member function call, as overload resolution might choose a
>> static member function that doesn't need 'this'.  The special 
>> handling
>> we want is for the case where the call depends on a generic lambda
>> parameter, in which case we capture 'this' because the call "names
>> [this] in a potentially-evaluated expression (3.2) where the 
>> enclosing
>> full-expression depends on a generic lambda parameter declared 
>> within
>> the reaching scope of the lambda-expression."
>>
> Good point.  I'll look into it.  So for a nullary member call we will
> always capture 'this', but for N-ary, we only capture if we find one
> of the lambda's parameters (or a parameter from an enclosing generic
> lambda?) in the call's arguments right?
>

Test like this?

/* { dg-do run { target c++14 } }  */
/* { dg-final { scan-assembler-not "..." } }  */

struct X
{
   int f (int, double) { return 255; }
   static int f (int, int) { return 65535; }

   auto m1 ()
   {
     return [=] (auto a) {
       return f (7, a);
     };
   }

   auto m2 ()
   {
     return [=] (auto a) {
       return f (9, 10) + a;
     };
   }
};

#include <cassert>

int main()
{
   X x;
   assert (x.m1 () (42.0) == 255);
   assert (x.m1 () (42) == 65535);
   assert (x.m2 () (42.0) == (65535 + 42));
   assert (x.m2 () (42) == (65535 + 42));
   assert (sizeof x.m2 () < sizeof x.m1 ());
}