Getting the error from __traits(compiles, ...)

[Bill Baxter]

On Fri, Nov 13, 2009 at 8:40 AM, bearophile <bearophileHUGS at lycos.com> wrote:
> Bill Baxter:
>> 2) how to get and report errors related to failure to compile some
>> code. (this one I hadn't thought of back then)
>
> I'd like a "static foreach" too. Eventually most statements will have a static version. At that point people will start seeing this little duplication in the language and someone may invent a way to throw away all the static versions and allow normal D code to be used at compile time, maybe with a 2-stage compilation or something.

A static switch would be nice too.   static if (is(type == xxx)) {}
else static if (is(type==yyy)) {} else static if ... gets kinda
tedious.


The kind of unification you're talking about is one thing I like about
Nemerle's 2-phase macros-as-plugins.  The code you execute at compile
time is written in exactly the same language as what you execute at
runtime.  And no CTFE engine is required to make it work.  Only one
new construct required, the macro facility itself.

But I don't think that leads to elimination static if, etc.  It just
means that such things become implementable as macros, rather than
language constructs.

On the other hand, having macros doesn't mean that you don't want
constant folding.  And if you can fold the constant 2+3, why not the
constant add(2,3)?  So desire to fold as many constants as possible
naturally leads to a desire to do CTFE and be able to execute your
entire language at compile time.

And once you're there -- yeh, I guess you're right.   Ultimately it's
not really necessary to specify static if vs regular if.   It's yet
another extension of constant folding -- if the condition is a compile
time constant, then it can act as a static if.   Same goes for loops.
But like regular loop unrolling optimizations, the compiler should
decide if it's prudent to unroll that 10,000 static foreach loop or
not.

So in short.  I think you're right.  "static if"  should go away.  But
"2-stage" compilation isn't really necessary, just more extensions to
the constant folding engine.  (Or perhaps you could say constant
folding is already a separate stage of a 2-stage process)

--bb