More range woes: composed ranges are unsafe to return from functions

[Brad Anderson]

On Tue, Oct 16, 2012 at 2:54 PM, H. S. Teoh <hsteoh at quickfur.ath.cx> wrote:

> On Tue, Oct 16, 2012 at 12:33:20PM -0700, H. S. Teoh wrote:
> [...]
> > Another data point: if I move the .joiner call out of cprod() into
> > main(), then there is no problem. Could it be that something in joiner
> > is breaking somehow, when returned from a function?
> [...]
>
> I found a reduced case:
>
>         import std.algorithm;
>         import std.range;
>         import std.stdio;
>
>         auto boo() {
>                 auto C = [2];
>                 return
>                         [1,1]
>                         .map!((a) => C)
>                         .joiner
>                 ;
>         }
>
>         void main() {
>                 auto C = [2];
>                 writeln(
>                         [1,1]
>                         .map!((a) => C)
>                         .joiner
>                 .take(12));
>
>                 writeln("====");
>
>                 writeln(boo().take(12));
>         }
>
> Excuse the odd formatting, I wanted to make sure the [1,1,1].map!(...)
> parts are line-for-line identical between boo() and main().
>
> This example segfaults in the last writeln. Commenting out .joiner makes
> the segfault go away. Reducing [1,1] to a 1-element array makes the
> problem go away. Replacing C with [1] makes the problem go away.
> Removing map!(...) and replacing it with something involving C makes the
> problem go away. Deleting the .take(12) outputs a whole mass of garbage
> values and then segfaults.
>
> So it seems like there is some kind of bad interaction between map and
> joiner. Maybe as jethro said, it's wrong code produced by dmd for the
> delegate passed to map? It seems to be dependent on the reference to the
> local variable C, which seems to imply a corrupted (or just
> out-of-scope?) delegate context.
>
>
> T
>
> --
> The best way to destroy a cause is to defend it poorly.


I'm starting to think maybe I shouldn't have closed my issue I reported
awhile back:

http://d.puremagic.com/issues/show_bug.cgi?id=7978

I really need to read how closures are supposed to work.

BA
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