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While looking at std::allocator, I see that members:value_type, pointer, const_pointer, reference, const_reference, size_type, difference_type, and rebind have all been deprecated.
Allocators will also no longer have the members:address, max_size, construct, or destroy.
Why did this happen? Did it have something to do with polymophic allocators?
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Member functions associated with std::allocator() : address: It is used for obtaining the address of an object although it is removed in C++20. construct: It is used to construct an object.It is also removed in C++20. destroy: It is used to destruct an object in allocated storage.It is also removed in C++20.
Allocators are used by the C++ Standard LibraryC++ Standard LibraryThe C++ Standard Library provides several generic containers, functions to use and manipulate these containers, function objects, generic strings and streams (including interactive and file I/O), support for some language features, and functions for everyday tasks such as finding the square root of a number.https://en.wikipedia.org › wiki › C++_Standard_LibraryC++ Standard Library - Wikipedia to handle the allocation and deallocation of elements stored in containers. All C++ Standard Library containers except std::array have a template parameter of type allocator<Type> , where Type represents the type of the container element.
If you look at the relevant isocpp paper you can see that the first set you mention is now thought to be better placed in std::allocator_traits. Since the STL (not even standard library) came out, there's been more of a shift to use traits.
rebind is also a relic. When the STL first came out, aliases and template-template parameters were not supported. With these language features in existence, rebind seems fairly convoluted. E.g., as you can see in an answer to this question, in The C++ Programming Language, 4th edition, section 34.4.1, p. 998, commenting the 'classical' rebind member in default allocator class :
template<typename U> struct rebind { using other = allocator<U>;}; Bjarne Stroustupr writes this : "The curious rebind template is an archaic alias. It should have been:
template<typename U> using other = allocator<U>; However, allocator was defined before such aliases were supported by C++."
So, altogether, it's the standard library catching up with the language and paradigm shifts.
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