why compiler can't deduce template argument in my code?

Question

I'm using visual studio and I've tried every thing I could think of. but don't know why this piece of code generates error, this is my code:

template <class A,class B> B returnArgtype(void (A::*)(B)) {return *new B;}

struct test
{
    void function(int);
    decltype(returnArgtype(&test::function)) x;
};

and it generates this error :

error C2784: 'A returnArgtype(void (__thiscall A::* )(B))' : could not deduce template argument for 'void (__thiscall A::* )(B)' from 'void (int)'

and I'm wondering it doesn't generate that error when parameter x is initializing inside a function, something like this:

struct test
{
    void function(int)
    {
        decltype(returnArgtype(&test::function)) x;
    }
};

Does the first one work if you say `&test::function`? – Kerrek SB Jul 04 '11 at 16:25 — Kerrek SB, Jul 04 '11 at 16:25
no, that was my copy-pasting error! – Ali1S232 Jul 04 '11 at 16:27 — Ali1S232, Jul 04 '11 at 16:27

Kerrek SB · Answer 1 · 2011-07-04T16:35:30.193

2

This works for me (GCC 4.6, -std=c++0x):

template <class A, class B> B returnArgtype(void (A::*)(B));

struct test
{
  void function(int);
  decltype(returnArgtype(&test::function)) x;
};

edited Jul 04 '11 at 16:35

answered Jul 04 '11 at 16:23

Kerrek SB

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It seems it only has problem on visual studio, I've tested that code on GCC myself and I didn't encounter any problems. I was looking for some answer to fix that in Visual studio. – Ali1S232 Jul 07 '11 at 18:39

score 1 · Accepted Answer · edited May 23 '17 at 12:13

This is the same bug I linked to on your other question (please upvote it to make it more likely MS will spend time fixing it):

C++ compiler loses member-ness of pointer-to-member-function during template deduction, causes ICE

Then, look at @Ise Wistera's answer which is much simpler and probably doesn't cause this problem.

Microsoft updated the bug report to say they've figured out a fix.

why compiler can't deduce template argument in my code?

2 Answers2