On 07.08.2013 20:56, Adam Butcher wrote:
On 07.08.2013 16:59, Jason Merrill wrote:
On 08/07/2013 03:52 AM, Adam Butcher wrote:
But a cleaner way might be to extend the "processing
template declaration" state from lambda declarator all the way to
the end of the
lambda body. This would match with the scenario that occurs with a
standard
in-class member function template definition. To do that elegantly
would
require a bit of refactoring of the lambda parser code.
It isn't already set through the whole lambda body?
No. It is within cp_parser_lambda_declarator_opt.
That seems
necessary to support non-trivial lambda bodies; otherwise we won't
be
able to handle dependence properly.
Agreed. Okay, I will produce three patches:
1) Refactor existing monomorphic implementation to give a cleaner
parser separation of concerns; extract the fco creation and
provide begin and end for the lambda function operator.
I did this---well not exactly as written---but I extended the template
decl state through until the end of the lambda body. And it works with
my dependence test. However, the previous version does too. The
following program works fine (conv ops an all) with the refactored
version and without it. I'm now questioning whether it is worth making
any change in this area. What do you think? The test code is as
follows and the resulting program correctly executes S::N::test() 4
times as expected -- were you thinking of some other dependence case?
#include <iostream>
struct S
{
struct N
{
float test () { std::cout << "S::N::test() -> 7.f\n"; return
7.f; }
};
};
int main()
{
auto f = [] <typename T> (T const& s) {
typename T::N x;
return x.test ();
};
auto g = [] (auto const& s) {
typename std::decay<decltype (s)>::type::N x;
return x.test ();
};
S i;
f(i);
g(i);
float (*pfn) (S const&) = f;
pfn(i);
pfn = g;
return pfn(i);
}
Error messages are reasonable also. Omitting the necessary 'typename's
gives:
: need ‘typename’ before ‘T::N’ because ‘T’ is a dependent scope
: need ‘typename’ before ‘typename std::decay<decltype
(s)>::type::N’ because ‘typename std::decay<decltype (s)>::type’ is a
dependent scope
Passing a local 'struct X {}' instead of 'S' gives:
: In instantiation of ‘auto main()::<lambda(const T&)> const [with T
= main()::X]’:
:24:9: required from here
:14:23: error: no type named ‘N’ in ‘struct main()::X’
...
So all seems to be okay with both versions. Any ideas why?
Cheers,
Adam
