[ConceptGCC]|
[ConceptGCC] |
ConceptGCC :Re: Requiring a function template specialization |
From: Tom Honermann (tom.honermann_at_[hidden])
Date: 2007-06-06 20:52:26
I'm not sure if that is sufficient. Consider this code:
#include <iostream>
template<typename T>
T foo() {
return 0;
}
template<>
int foo<int>() {
return 1;
}
int foo() {
return 2;
}
int main() {
std::cout << "foo<char>(): " << (int)foo<char>() << std::endl;
// writes 0
std::cout << "foo<int>(): " << foo<int>() << std::endl;
// writes 1
std::cout << "foo(): " << foo() << std::endl;
// writes 2
// With out the non-template 'int foo()' above, this last line
won't compile
// (error: no matching function for call to `foo()')
return 0;
}
Compiled with conceptgcc-boostcon (g++, not conceptg++) on Linux, this
produces
foo<char>(): 0
foo<int>(): 1
foo(): 2
It is conceivable that a concept may require both the template
specialization and non-template functions to exist. In this case, the
caller needs to make the call explicit - which would require template
syntax. Alternatively, a concept_map could potentially handle this, but
that doesn't feel right to me - how would it know whether the call
should be satisfied by a template or non-template function?
Tom.
Douglas Gregor wrote:
>On Jun 6, 2007, at 4:36 PM, Walter E Brown wrote:
>
>
>
>>I would like to express a concept, Foo<T>, that requires the existence
>>of a specialization, foo<T>, of a function template.
>>
>>I tried the following with conceptgcc-boostcon under Cygwin, but
>>got an
>>ICE (I submitted a bug report earlier today):
>>
>> #include <concepts>
>>
>> concept Foo< class T >
>> {
>> template<>
>> T
>> foo<T>();
>> };
>>
>>Is the above the correct way to express the desired concept? Thanks,
>>
>>
>
>A template specialization has to specialize something. In this case,
>there is no primary template to be specialized. One thing you can do
>is write this:
>
> concept Foo<class T> {
> T foo();
> }
>
>You can call it as just "foo()", or (to be more specific), Foo<T>::foo
>().
>
> - Doug
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>
>
-- Oracle Email Signature Logo Tom Honermann | Senior Principal Software Engineer | 503.276.2354 Oracle PeopleTools Development 1211 SW 5th Ave, Suite 9080, Portland, OR 97204
