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

[Andrei Alexandrescu]

Bill Baxter wrote:
> 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)


"static if" is different from "if" in the way it handles scopes. Also, 
the former is a declaration, the latter is a statement.

Andrei