Allocators

Recall: STL separates contained objects' constructor and memory allocation.
Allocators required in environments with multiple memory models (16 bit PCs).
Allocators may also be useful for fixed-memory applications, OO database interfaces, and parallel processing.

Allocators (cont.)

Kludge! Every STL container class is supposed to be parameterized with an allocator template class (with a default value). For example, list should be declared as:
```
   template < class T, template < class U > Alloc = allocator >
   class list { ...
   
```
So you can declare a list either way:
```
   list< int > a;
   list< int, far_allocator > b;
   
```
But most compiler don't yet support default template arguments that are templates themsleves. So the kludge is that the allocator is handled by the preprocessor. Very limiting.