On Mon, 19 Oct 2009 21:50:46 -0400, Walter Bright
<[email protected]> wrote:
Currently, static arrays are (as in C) half-value types and
half-reference types. This tends to cause a series of weird problems and
special cases in the language semantics, such as functions not being
able to return static arrays, and out parameters not being possible to
be static arrays.
Andrei and I agonized over this for some time, and eventually came to
the conclusion that static arrays should become value types. I.e.,
T[3]
should behave much as if it were:
struct ??
{
T[3];
}
Then it can be returned from a function. In particular,
void foo(T[3] a)
is currently done (as in C) by passing a pointer to the array, and then
with a bit of compiler magic 'a' is rewritten as (*a)[3]. Making this
change would mean that the entire array would be pushed onto the
parameter stack, i.e. a copy of the array, rather than a reference to it.
Making this change would clean up the internal behavior of types.
They'll be more orthogonal and consistent, and templates will work
better.
The previous behavior for function parameters can be retained by making
it a ref parameter:
void foo(ref T[3] a)
What happens for IFTI?
void foo(T)(T t)
{
return t[2];
}
void main()
{
int[3] x;
x[] = 5;
printf(foo(x));
}
I would think T would resolve to int[3], which means pass by value. You'd
need a specialization for static arrays to get the current behavior.
Don't get me wrong, I would love to see static arrays become real types,
but I wonder if there are any ways we can "optimize out" the staticness of
an array argument for templates. In particular, I hate how IFTI likes to
assume static array for literals...
In the absence of such an optimization, I'd still prefer static arrays
become value types like you say.
-Steve
