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src/secure_allocator.hpp: define missing 'rebind' type #4480

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Dec 22, 2022
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src/secure_allocator.hpp: define missing 'rebind' type #4480

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11 changes: 11 additions & 0 deletions src/secure_allocator.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -99,6 +99,17 @@ bool operator!= (const secure_allocator_t<T> &, const secure_allocator_t<U> &)
#else
template <typename T> struct secure_allocator_t : std::allocator<T>
{
secure_allocator_t () ZMQ_DEFAULT;

template <class U>
secure_allocator_t (const secure_allocator_t<U> &) ZMQ_NOEXCEPT
{
}

template <class U> struct rebind
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@jwakely jwakely Dec 20, 2022 •
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Suggested change
template <class U> struct rebind
secure_allocator_t() { }
template<class U> secure_allocator_t(const secure_allocator_t<U>&) { }
template <class U> struct rebind

The error is because you need a converting constructor that can be used to construct Alloc<U> from Alloc<T> and vice versa. This adds it.

The other requirements for an allocator type are value_type, allocate and deallocate, and operator== which can both come from the std::allocator base class.

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became special

It didn't.

To rebind an allocator you need to be able to determine the rebound type, and construct an instance of the rebound type from the original type. With the missing rebind the rebound type is std::allocator<U> and that can be constructed from a secure_allocator_t<T> (via slicing). But that's broken.

With the new rebind member the rebound type is correct: secure_allocator_t<U>. But you can't construct that from secure_allocator_t<T>. So you need to add a converting constructor, and then you also need a user-declared default constructor.

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Thank you! Taken default constructor and conversion constructor definitions from the non-no-op variant as well. I think it is equivalent to the definition you suggested.

{
typedef secure_allocator_t<U> other;
};
};
#endif
}
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