On 05/29/2013 03:59 PM, Peter Williams wrote:
> I've been trying to find out how non ref array arguments are passed to
> functions in D but can't find any documentation on it.
The following concepts are relevant:
- Dynamic array: Maintained by the D runtime
- Fixed-length array (aka static array): Can be on the stack
- Slice: An efficient tool to access a range of elements (of any type of
array)
Usually, it is the slice that gets passed:
void foo(int[] slice);
A slice is made up of the pointer to the first element and the number of
elements:
struct __SomeImplementationDependentName__
{
size_t length;
void * ptr;
}
When you pass a slice by-value, as in the case of foo() above, that
struct gets copied: a copy of the argument...
So, slice variables have value semantics but they are used as references
to elements.
Fixed-length arrays are a different story: Unlike C arrays and unlike D
slices, the elements are always copied.
> If doing that is not much less efficient than passing by ref (and
isolates
> the external representation of the array from anything I do) then I
can stop
> using ref and the problem goes away.
Yes, simply pass-by-reference. Not expensive at all. There may be
surprises though; you may want to read this article:
http://dlang.org/d-array-article.html
Ali
