funny bug with input range interface and toString

[Nick Voronin]

On Mon, 13 Dec 2010 11:24:48 +0300, spir <denis.spir at gmail.com> wrote:

> I have a strange bug with an input range interface. Initially, I had a  
> (rather big) struct called Text with loads of working unittests. When  
> adding a range interface, noting worked anymore, any test ran into an  
> infinite loop (the terminal writes pages of '[') ending with segfault.

     @property Text front () {
         return Text(this.stacks[this.rangeIndex]);
     }

Um. There is recursion. front() of Text returns Text. formatValue iterates  
through Range, trying to format every element of it... but goes nowhere  
because Range.front never yields anything but itself typewise.

> After shrinking the bug's scope,I finally found it happens on simple  
> writeln(text).

Not so simple, with all underlying mess of templates :-D I suppose it's a  
bug that instantiation of formatValue for Range types there always tries  
to iterate manually, ignoring existing toString.

void formatValue(Writer, T, Char)(Writer w, T val,
         ref FormatSpec!Char f)
if ( ( is(T == struct) || is(T == union) ) && !isInputRange!T)

As you can see it even explicitly mention that default formatting for  
struct (which can use toString) not to be used for Ranges. I think it's  
wrong.

> https://bitbucket.org/denispir/denispir-d/changeset/39200b499fb9#chg-textbug.d.  
> Note that the range interface itself works fine.

btw, I wonder, how do you build it? I ended up with very long command line  
for dmd, as there was no makefile and jake/rdmd failed to produce anything  
ether.

> So, it seems that, in my case for any reason, introducing an input range  
> lets D shortcut toString (and try to use what instead?). Look like a bug?

Yup! Still, stack overflow is due to unconventional Range interface.

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