Is there an easy way to convert a pointer to malloc'd memory to an array?

[ZombineDev via Digitalmars-d-learn]

On Tuesday, 24 May 2016 at 18:42:41 UTC, Gary Willoughby wrote:
> I have a T* pointer to the start of a malloc'd chunk of memory, 
> the type T and the number of T's stored in the chunk.
>
> Is there an efficient way of converting this information to a D 
> array of type T[] or even T[n]?

BTW, the simplest way to use C malloc to allocate and initialize 
a D array is with 
http://dlang.org/phobos/std_experimental_allocator#makeArray:

struct MyObj { /* ... */ }

{
     MyObj[] arr = Mallocator.instance
         .makeArray!MyObj(10, ctorArgs);
     scope (exit) Mallocator.instance.dispose(arr);

     // use arr...

} // arr is freed at the end of the scope

Which is rougly equivalent to:

void* p = malloc(10 * MyObj.sizeof);
T[] arr = (cast(T*)p)[0 .. 10];
foreach (ref elem; arr)
     emplace(elem, ctorArgs);

The benfit of using make* and dispose is that they allow you to 
change the allocator if you so need. You can also use the GC:
int[] arr = GCAllocator.instance.makeArray!int(128);
// no need to free arr

The common idiom is that the user of a function that produces an 
array should supply the allocator as a parameter through which 
the function will make allocations. This useful when you know for 
example that the allocation would be small and short-lived in 
which case it would better to use a stack allocator, rather than 
a heap allocator.