Currently, builtin arrays enjoy the restriction that you cannot ref the index parameter when doing a foreach:
int main(string[] args)
{
foreach(ref i, ref s; args) // Error: foreach: key cannot be out or ref
{ }
}
But when trying to do something similar on a struct, the compiler cannot resolve the opApply:
struct S
{
int[] arr;
int opApply(int delegate(int i, ref int v) dg)
{
int result = 0;
foreach(i, ref x; arr)
{
if((result = dg(i, x)) != 0)
break;
}
return result;
}
}
void main()
{
S s;
foreach(i, ref v; s)
{}
}
emits:
testit.d(32): function testit.S.opApply (int delegate(int i, ref int v) dg) does not match parameter types (int delegate(ref int __applyArg0, ref int v))
testit.d(32): Error: cannot implicitly convert expression (__foreachbody1) of type int delegate(ref int __applyArg0, ref int v) to int delegate(int i, ref int v)
This has implications for const as well, because it would make sense in S above to have an opApply WITHOUT a ref int for the value in the case of a const S.