SFINAE

[Jason House]

Now that we're all talking about templates and Andrei is participating on
this list, I figure it's a good time to bring this topic up again.

(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)

SFINAE causes debugging nightmares with template based code when a
specialization fails to compile as expected.  When I challenged people in
the past to provide real examples of template code that would require
SFINAE in D, nobody could come up with one.  The template declaration and
constraints in D seem to be enough.

I think we should try removing SFINAE from 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 think
it may be better to enhance existing generic programming techniques than to
keep SFINAE.  The further SFINAE gets pushed out of normal use (through
constraints and detailed type declarations), the more of a corner case
SFINAE becomes.  The more this happens, the more this "feature" will bite
developers instead of helping them.

PS: This is basically a rehash of what I typed in
http://d.puremagic.com/issues/show_bug.cgi?id=1951

It's also based on the past newsgroup thread at
http://digitalmars.com/d/archives/digitalmars/D/SFINAE_is_Evil_67995.html