Compile time code paths

[Jeremie Pelletier]

David Gileadi Wrote:

> Daniel Keep wrote:
> > Jeremie Pelletier wrote:
> >> If a function has both an asm and D implementations inside its body, and the D version can be executed at compile time, but the asm one is much faster at runtime. Is it possible to have the compiler use the D code path at compile time (ie to fill in enums and whatnot), and have the asm version available at runtime.
> > 
> > Not that I know of.  There's no way to switch based on run time/compile
> > time.  This was going to be solved, at least in part, using static
> > arguments, but that got dropped.
> > 
> > As it stands, you just have to use a suffix or prefix or something to
> > distinguish CTFE methods from runtime methods.
> 
> Is this a case for version(CompileTime){}?

No because it would also compile this block into the binary. 

The easy way is of course to have different symbols for compile-time and run-time. But this doesn't go well with generic programming where the function needing such a check can be deep in the compile-time call stack.

For example:
int foo() { return bar + 1; }
int bar() { return foobar * 2; }
int foobar() {
static if(isCompileTime) return ...; /// asm cannot execute at compile time, needed to keep foo and bar able to do CTFE
else asm { ...; } /// asm optimized for runtime
}