On Thu, 07 Oct 2010 10:43:25 -0400, Benjamin Thaut
<[email protected]> wrote:
If I want to tell the compiler that a certain function argument should
not be
copied (say a large struct, or a array) which is the right way to do?
arrays:
1. function foo(in float[] bar) { ... }
2. function foo(ref const(float[]) bar) { ... }
3. something else
Arrays are passed by pseudo-reference. That is, the data is passed by
reference, but what part of the data is referred to is passed by value.
so passing an array without any adornments will not copy the array data.
example:
void foo(int[] x)
{
x = x[3..4]; // does not affect caller's copy
x[0] = 5; // does affect caller's copy
}
void bar()
{
int[] x = new int[10];
foo(x);
assert(x.length == 10);
assert(x[3] == 5);
}
structs:
1. function foo(in largestruct bar) { ... }
2. function foo(ref const(largestruct) bar) { ... }
3. something else
Structs are copied by value, but only a shallow copy. So if your struct
is large, you probably want to use ref. But if your struct is 'large'
because it contains references to large pieces of data, passing by value
is ok (similar to arrays).
As a note, in means const scope. So in largestruct bar is equivalent to
scope const largestruct bar. The scope does nothing, so this can be
reduced to const largstruct bar. This does not pass by reference.
-Steve
