[Issue 6967] New: template instantiation depends an pragma(msg, T.stringof) if __traits is used

[d-bugmail at puremagic.com]

http://d.puremagic.com/issues/show_bug.cgi?id=6967

           Summary: template instantiation depends an pragma(msg,
                    T.stringof) if __traits is used
           Product: D
           Version: D2
          Platform: Other
        OS/Version: Linux
            Status: NEW
          Severity: normal
          Priority: P2
         Component: DMD
        AssignedTo: nobody at puremagic.com
        ReportedBy: tobias at pankrath.net


--- Comment #0 from Tobias Pankrath <tobias at pankrath.net> 2011-11-17 09:41:24 PST ---
>From a thread in d.learn:
http://www.digitalmars.com/d/archives/digitalmars/D/learn/Strange_behaviour_in_templates_Another_bug_30591.html


I'm trying to learn template meta programming in D. To do this, I'm working
on a  meta state machine like Boost.MSM 
(http://www.boost.org/doc/libs/1_47_0/libs/msm/doc/HTML/index.html).

States are types and can have sub states. If they do, they need to have
an attribut 'SubStates', which should be a TypeTuble with the 
sub states.

The task at hand is: Given a State and a list of all States, create
a list of all parents of State including State itself.

This code (http://paste.pocoo.org/show/506154/) ought to do this
and it works sometimes. 

You can make to interesting observations of this code:

In its current form, 'dmd test.d -unittest' will print: "
> false

But if you uncomment the first pragma() in the unittest block,
it will print 
> () 
> true

If you change the body of ParentsDesc to 
> alias TypeTuple!() Result;
it will also print
> true

Although the static if in ParentsDesc is never true in this
example.

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