std::pair allocator?

[Mark P]

Why doesn't std:air have an allocator?

 

[codigo]

Why doesn't std:air have an allocator?

A std:air is not a container. Its purpose is not to allocate. Think of a
std:air as a record-template for inserting or extracting a record-pair to
/ from a given associative container. Its the associative container that
handles or stores the allocation of a std:air's contents.

 

[Andrew Koenig]

Why doesn't std:air have an allocator?

If it had one, how would it use it?

 

[Ron Natalie]

Why doesn't std:air have an allocator?

Because it doesn't allocate anything.

 

[Mark P]

If it had one, how would it use it?

I'm not sure I read on the SGI website, "A pair is much like a
Container, in that it 'owns' its elements." But I guess the concept of
an allocator only makes sense for containers which can grow in size or
contents, whereas any pair instance is of a fixed size?

 

[James Dennett]

I'm not sure I read on the SGI website, "A pair is much like a
Container, in that it 'owns' its elements." But I guess the concept of
an allocator only makes sense for containers which can grow in size or
contents, whereas any pair instance is of a fixed size?

Right. Dynamic allocation isn't needed when the number of items
is known at compile time (though in other such cases it may be
desirable for other reasons, such as limited stack space).

-- James

 

[Rolf Magnus]

I'm not sure I read on the SGI website, "A pair is much like a
Container, in that it 'owns' its elements." But I guess the concept of
an allocator only makes sense for containers which can grow in size or
contents, whereas any pair instance is of a fixed size?

Basically, yes. allocators give containers a way to (surprise!) allocate
memory, but std:air doesn't allocate memory. It's basically just
something like:

template <typename First, typename Second>
struct pair
{
First first;
Second second;
};

Not really much use for an allocator here. ;-)