On 02/11/2011 05:27 AM, Jesse Phillips wrote:
spir Wrote:
But in your example the symbol a does not look like a constant, instead it the
loop variable. Do, how does it work?
Magic.
No really, the best I can tell is that the compiler will try to run the foreach
loop at compile-time if there is something in the body that must be evaluated
at compile time.
The type you are iterating over must be known at compile-time, and just like
any such value it is identified by its type and not its contents. So your array
literal could in fact be built with a variable, the fact that it is not doesn't
matter.
I'm not sure if much thought has gone into compile-time-looping, the best way to enforce
it is to get a function to run at compile time. I think the rule of "when the body
needs evaluated at compile-time" is what's used, but this also means that when you
try to iterate something like __traits or tupleof and don't use a compile-time construct
in the body, you don't get an error or the loop executed.
Oh yes, I see. This explains why my example using plain constants (predefined
values, thus known at compile-time) does not run: there is nothing /forcing/
the compiler (such as a ref to a type), thus the compiler does not even try.
Even if would be less complicated, probably, than with __traits.
Denis
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