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Re: On stateful allocators and GCC

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On 9/11/2019 1:32 PM, Daniel wrote:
> On Wednesday, September 11, 2019 at 5:04:43 AM UTC-4, Juha Nieminen wrote:
>> Daniel wrote:
>>> I have no issues with vs or clang.
>>
>> I tried this with clang, and it gives an error. (If the constructor is
>> commented out, it compiles and works ok.) Am I missing something obvious?
>>
>> //-----------------------------------------------------
>> #include <iostream>
>> #include <string>
>>
>> struct MyAlloc
>> {
>>      using value_type = char;
>>      MyAlloc(int) {}
>>      char* allocate(std::size_t n) { return new char[n]; };
>>      char* allocate(std::size_t n, const void*) { return new char[n]; };
>>      void deallocate(char* ptr, std::size_t) { delete[] ptr; }
>>      bool operator==(const MyAlloc&) const { return true; }
>>      bool operator!=(const MyAlloc&) const { return false; }
>> };
>>
>> int main(int argc, char** argv)
>> {
>>      std::basic_string<char, std::char_traits<char>, MyAlloc> str("hello");
>>      std::cout << str << "\n";
>> }
>> //-----------------------------------------------------
> 
> For a stateful allocator, you need to pass an instance of the constructor
> to the object.
You probably meant to pass an instance of the allocator.
In C++ an instance of the constructor is ungood.

  But MyAlloc also isn't right, it needs to be a template class,
> and have a constructor that supports rebinding. As a minimal example, try
> 
> #include <iostream>
> #include <string>
> #include <memory>
> 
> template <class T>
> struct MyAlloc
> {
>      using value_type = T;
>      using size_type = std::size_t;
>      using propagate_on_container_move_assignment = std::true_type;
> 
>      MyAlloc(int) {}
> 
>      template< class U >
>      MyAlloc(const MyAlloc<U>&) noexcept {}
> 
>      T* allocate(size_type n)
>      {
>          return static_cast<T*>(::operator new(n * sizeof(T)));
>      }
> 
>      void deallocate(T* ptr, size_type) noexcept
>      {
>          ::operator delete(ptr);
>      }
> 
>      bool operator==(const MyAlloc&) const { return true; }
>      bool operator!=(const MyAlloc&) const { return false; }
> };
> 
> int main()
> {
>      std::basic_string<char, std::char_traits<char>, MyAlloc<char>> str("hello", MyAlloc<char>(1));
>      std::cout << str << "\n";
> }
> 
> 

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On stateful allocators and GCC Daniel <danielaparker@gmail.com> - 2019-09-09 20:54 -0700
  Re: On stateful allocators and GCC Melzzzzz <Melzzzzz@zzzzz.com> - 2019-09-10 04:00 +0000
    Re: On stateful allocators and GCC James Kuyper <jameskuyper@alumni.caltech.edu> - 2019-09-10 08:56 -0400
  Re: On stateful allocators and GCC Öö Tiib <ootiib@hot.ee> - 2019-09-10 00:25 -0700
    Re: On stateful allocators and GCC Öö Tiib <ootiib@hot.ee> - 2019-09-10 01:04 -0700
      Re: On stateful allocators and GCC Daniel <danielaparker@gmail.com> - 2019-09-10 04:51 -0700
    Re: On stateful allocators and GCC Daniel <danielaparker@gmail.com> - 2019-09-11 04:39 -0700
  Re: On stateful allocators and GCC Juha Nieminen <nospam@thanks.invalid> - 2019-09-11 09:04 +0000
    Re: On stateful allocators and GCC Daniel <danielaparker@gmail.com> - 2019-09-11 04:32 -0700
      Re: On stateful allocators and GCC Manfred <noname@add.invalid> - 2019-09-11 15:02 +0200
        Re: On stateful allocators and GCC Daniel <danielaparker@gmail.com> - 2019-09-11 06:33 -0700

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