pure and custom new / delete

[Steven Schveighoffer]

On Tue, 26 Jun 2012 12:05:55 -0400, Benjamin Thaut  
<code at benjamin-thaut.de> wrote:

> Am 26.06.2012 18:02, schrieb Timon Gehr:

>> You can cast function pointers to pure, or mark extern(C) memory
>> allocation functions as pure.
>
> extern(c) is not an options as there is a structure of various different  
> allocators that implement a common interface which all is written in D.

extern(C) does not mean implemented in C, it just means C linkage.  You  
can use arrays, classes, etc. in extern(C) functions.  UFCS makes this  
really easy too:

myalloc.d:

interface Allocator
{
    void * _alloc(size_t size);
}

extern(C) void *alloc(Allocator a, size_t size) pure;

allocimpl.d:
import myalloc;

extern(C) void *alloc(Allocator a) // pure
{
    return a._alloc(size)
}

mallocer.d:

public import myalloc;
import std.c.stdlib;

// sample allocator
class Mallocer : Allocator
{
    void *_alloc(size_t size) { return malloc(size);}
}

main.d:

import mallocer;

void foo(Allocator a) pure
{
    a.alloc(200);
    //a._alloc(200); // fails as expected
}

void main()
{
    foo(new Mallocer);
}

-Steve