On Fri, 04 Nov 2011 09:01:11 -0400, Christophe
<[email protected]> wrote:
"Steven Schveighoffer" , dans le message (digitalmars.D:146563), a
écrit :
The foreach delegate syntax already allow you to have parametrized
iteration over a structure !
Actually, the delegate do not have to be returned by the & operator, it
can be returned by a function. It's a bit awkward first, but then it's
easy to use:
struct Iterable
{
int delegate(int delegate(ref int)) inReverse()
{
return ()
{
int result = 0;
foreach(int i; 0..100)
{
auto t = 99-i;
if((result = dg(t)) != 0) break;
}
return result;
}
}
int delegate(int delegate(ref int)) byStep(int step)
{
return()
{
int result = 0;
foreach(int i; iota(0, 100, step))
{
auto t = i;
if((result = dg(t)) != 0) break;
}
return result;
}
}
}
int main()
{
Iterable it;
foreach (i; it.inReverse) writeln(i);
foreach (i; it.byStep(2)) writeln(i);
}
There is no need to add a special syntax to do what you want !
Maybe there should be a bit more documentation about this.
I'll point out first that this solution allocates a closure on the heap --
not necessarily the most efficient solution.
Second of all, this seems like a *lot* of trouble to go through just to
call a function (yes, that's all you're doing). The delegate returned is
called *once* and then thrown away.
I'd much rather the language just support the most straightforward
solution (calling a function with the given parameters).
-Steve
