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Re: Is this valid C++ code?

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On 10/4/2022 1:47 PM, Bo Persson wrote:
> On 2022-10-03 at 23:09, daniel...@gmail.com wrote:
>> Hello everyone,
>>
>> Is the C++ code below valid?
>>
>> #include <iostream>
>> #include <string_view>
>> #include <string>
>>
>> template <class T, class Enable = void>
>> class Foo
>> {};
>>
>> template <class T>
>> class Foo<T,typename 
>> std::enable_if<std::is_same<T,std::string>::value>::type>
>> {
>> public:
>>      void f(std::string s)
>>      {
>>          Foo<std::string_view> foo; // (*)
>>          foo.f(s);
>>      }
>> };
>>
>> template <class T>
>> class Foo<T, typename std::enable_if<std::is_same<T, 
>> std::string_view>::value>::type>
>> {
>> public:
>>      void f(std::string_view s)
>>      {
>>          std::cout << s << "\n";
>>      }
>> };
>>
>> int main()
>> {
>>      Foo<std::string> foo;
>>      foo.f("Hello World");
>> }
>>
>> LLVM (clang-cl) says "yes", and outputs "Hello World".
>>
>> Visual Studio 2022 (v143) says "no", "'f': is not a member of 
>> 'Foo<std::basic_string_view<char,std::char_traits<char>>,void>",        17
>> at line (*)
>>
>> Both compiled with C++17.
>>
> 
> Seems like g++ (v12.2) agrees with VC++, and also points out the problem 
> that the specialization is defined after its first use.
> 
> My (non-language-lawyer) interpretation is that since f and its local 
> foo don't depend on the template parameter T, they should be looked up 
> immediately, and not at the point of instantiation.
> 
> 

A good example of when someone's question, and its answer, are useful 
for someone else too.
Thanks.

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Is this valid C++ code? "daniel...@gmail.com" <danielaparker@gmail.com> - 2022-10-03 14:09 -0700
  Re: Is this valid C++ code? David LaRue <huey.dll@tampabay.rr.com> - 2022-10-03 23:52 +0000
    Re: Is this valid C++ code? "daniel...@gmail.com" <danielaparker@gmail.com> - 2022-10-03 18:07 -0700
      Re: Is this valid C++ code? "daniel...@gmail.com" <danielaparker@gmail.com> - 2022-10-03 18:42 -0700
    Re: Is this valid C++ code? Juha Nieminen <nospam@thanks.invalid> - 2022-10-04 06:05 +0000
  Re: Is this valid C++ code? Bo Persson <bo@bo-persson.se> - 2022-10-04 13:47 +0200
    Re: Is this valid C++ code? "daniel...@gmail.com" <danielaparker@gmail.com> - 2022-10-04 05:22 -0700
    Re: Is this valid C++ code? Manfred <noname@add.invalid> - 2022-10-05 02:54 +0200
  Re: Is this valid C++ code? Andrey Tarasevich <andreytarasevich@hotmail.com> - 2022-10-07 12:41 -0700
    Re: Is this valid C++ code? Andrey Tarasevich <andreytarasevich@hotmail.com> - 2022-10-08 11:18 -0700

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