• d-bugmail puremagic.com Mar 26 2008
• d-bugmail puremagic.com Mar 27 2008

d-bugmail puremagic.com writes:

http://d.puremagic.com/issues/show_bug.cgi?id=1951

           Summary: Remove SFINAE
           Product: D
           Version: unspecified
          Platform: All
        OS/Version: Linux
            Status: NEW
          Severity: enhancement
          Priority: P2
         Component: DMD
        AssignedTo: bugzilla digitalmars.com
        ReportedBy: jason.james.house gmail.com


I can imagine the request sounding almost crazy, but it really isn't.
(brief background: SFINAE = substitution failure is not an error.  Commonly
used when selecting which templated definition to apply.  Most uses in C++ are
tricks to determine info available in D is expressions)

I've been polling people on the D mailing list and those I know who are deep
into C++, and so far nobody can come up with a real-world use for SFINAE that
can't be done with other mechanisms already in D (is expressions, static if,
etc...)

What I have been able to find out from people is that SFINAE does cause
debugging nightmares with template based code when a specialization fails to
compile as expected.

I think trying no SFINAE is a great thing to try in D 2.x while it's still
considered experimental/alpha.  I expect a lack of SFINAE to make the compiler
simpler and ensure D preserves its fast compile times.

If it does turn out that SFINAE does provide unique functionality (I expect
Andrei may know), I think it may be better to enhance existing generic
programming techniques than to keep SFINAE.  The further SFINAE gets pushed out
of normal use, the more of a corner case it becomes...  biting developers more
often than it helps them.


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d-bugmail puremagic.com writes:

http://d.puremagic.com/issues/show_bug.cgi?id=1951





------- Comment #1 from wbaxter gmail.com  2008-03-27 03:26 -------
A good suggestion made on the newsgroups was to first add a switch to D2 for a
while that can be used to either disable SFINAE or to print out a trace message
every time the compiler uses it.


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