Re: template argument deduction oddity?
news.nospam.cechner@gmail.com writes:
This is not a big complicated generic thing, but the compiler is
having some trouble.
template <class D>
struct GenericThing
{
struct T { };
};
struct Stream
{ };
template <class D>
Stream& operator<< (
Stream& out,
typename GenericThing<D>::T const & thing)
{
return out;
}
int main()
{
GenericThing<int>::T t;
Stream s;
s << t;
}
I get this error in MSVC++ (similar problems in GCC) on the last line
in main:
error C2783: 'Stream &operator <<(Stream &,const GenericThing<D>::T
&)' : could not deduce template argument for 'D'
So what rule of C++ is preventing this deduction?
None. There's no rule in C++ that causes the deduction to happen.
I presume it has something to do with the argument type being
*inside* the template class as opposed to *being* the templated
type.
And how would one get around this problem?
You could use a traits based approach.
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