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[allocator.requirements.general] Consider changing Example 2 #5479

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frederick-vs-ja opened this issue May 20, 2022 · 4 comments · Fixed by #5482
Closed

[allocator.requirements.general] Consider changing Example 2 #5479

frederick-vs-ja opened this issue May 20, 2022 · 4 comments · Fixed by #5482

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@frederick-vs-ja
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The example seemly contains some "legacy" styles:

  • typedef: now using is preferred;
  • operator!=: as of C++20, rewritten candidates are generally preferred;
  • globally visible equality operators: hidden friends seem preferred.

Should we change the example as following to encourage preferred styles?

template<class Tp>
struct SimpleAllocator {
  using value_type = Tp;
  SimpleAllocator(ctor args);

  template<class T> SimpleAllocator(const SimpleAllocator<T>& other);

  [[nodiscard]] Tp* allocate(std::size_t n);
  void deallocate(Tp* p, std::size_t n);

  template<class T>
  friend bool operator==(const SimpleAllocator&, const SimpleAllocator<T>&);
};
@jensmaurer
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@jwakely , what do you think?

@jwakely
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jwakely commented May 20, 2022

I think a normal member instead of hidden friend would be simpler for the equality op. It can even be a non-template, and rely on the converting constructor.

bool operator==(const SimpleAllocator&) const;

@jwakely
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jwakely commented May 20, 2022

While we're here, should we use different template parameter names? Tp and T are unnecessarily similar. Maybe T and U.

@jwakely
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jwakely commented May 20, 2022

So:

template<class T>
struct SimpleAllocator {
  using value_type = T;
  SimpleAllocator(ctor args);

  template<class U> SimpleAllocator(const SimpleAllocator<U>& other);

  [[nodiscard]] T* allocate(std::size_t n);
  void deallocate(T* p, std::size_t n);

  bool operator==(const SimpleAllocator&) const;
};

@frederick-vs-ja frederick-vs-ja mentioned this issue May 21, 2022
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[allocator.requirements.general] Simplify SimpleAllocator with some new styles frederick-vs-ja/draft
3 participants
@jwakely @frederick-vs-ja @jensmaurer