• via Digitalmars-d-bugs (54/54) Jun 22 2016 https://issues.dlang.org/show_bug.cgi?id=16193

via Digitalmars-d-bugs <digitalmars-d-bugs puremagic.com> writes:

https://issues.dlang.org/show_bug.cgi?id=16193

          Issue ID: 16193
           Summary: opApply() doesn't heap allocate closure
           Product: D
           Version: D2
          Hardware: x86_64
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P1
         Component: dmd
          Assignee: nobody puremagic.com
          Reporter: schuetzm gmx.net

// yy.d
module yy;

struct S {
    int opApply(int delegate(int) dg) {
        foreach(i; 1 .. 10) {
            int result = dg(i);
            if(result) return result;
        }
        return 0;
    }
}


// xx.d
import yy;

int* px, py;

int foo() {
    int x = 0, y = 0;
    foreach(i; S.init) {
        px = &x; py = &y;
        y++;
    }
    return y;
}

void main() {
    import std.stdio;
    writeln(foo());
    int z = 0;
    writeln("&x = ", px, " &y = ", py, " &z = ", &z);
}


# dmd -c xx.d
# dmd -c yy.d
# dmd -ofxx xx.o yy.o
# ./xx

prints:
9
&x = 7FFEAD3C47C0 &y = 7FFEAD3C47C4 &z = 7FFEAD3C47E8
(or similar)

As can be seen, all local variables are allocated next to each other, evidently
on the stack. This happens even though S.opApply() doesn't take its delegate as
scope. I'm deliberately using separate compilation here to make sure that the
compiler has no way to infer that the closure doesn't escape.

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