Hello Steve,
foreach/opApply
Would it be a) true, and b) helpful if the documentation said
something like:
The body of the apply function iterates over the elements it
aggregates, passing them each to the dg function,
an implementation of
which is provided by the compiler for each opApply overload it
encounters.
I'm not shure that bit is correct. I'm not shure what you are saying.
If the dg returns 0, then foreach goes on to the next
element. If the dg returns a nonzero value, as it will if, for
example, a break or goto statement is executed in the loop, then apply
must cease iterating and return that value. Otherwise, after iterating
across all the elements, apply will return 0.
The class need not contain an aggregate. The values iterated can be
calculated in opApply from other class members, though there should be
a corresponding class member because of the ref in dg. The following
example should make the operation of foreach/opApply clear:
import std.stdio;
class Foo
{
uint orig;
uint cur;
this(uint n) { orig = n; cur = n; }
int opApply(int delegate(ref uint) dg)
{
writefln("enter opApply");
int result = 0;
for (int i = 0; i < 50; i++)
{
result = dg(cur);
writefln("Result %d", result);
if (result)
{
writefln(i);
cur = orig;
break;
}
cur += cur*3;
}
writefln("leave opApply");
return result;
}
}
void main()
{
Foo foo = new Foo(3);
foreach(uint u; foo)
{
writefln(u);
if (u > 200) goto L1;
}
L1:
foreach(uint u; foo)
{
writefln(u);
if (u > 10000) break;
}
foreach(uint u; foo)
{
writefln(u);
if (u > 10000) break;
// The delegate takes a ref uint
u = 0;
writefln(u);
}
}
