On Fri, 20 Apr 2012 15:21:12 -0400, Robert Clipsham
<[email protected]> wrote:
I've been staring blankly at this for a while now and want some input
from others:
----
void foo(T, U...)(bool arg)
{
if (arg)
{
assert(T.tupleof.length == U.length);
assert(arg); /* Line 6 */
// Or some other code here
}
}
struct A {}
void main()
{
foo!(A, int)(false);
}
----
When compiled with warnings:
$ dmd -w test.d
test.d(6): Warning: statement is not reachable
So what appears to be happening here is that dmd is constant folding
T.tupleof.length == U.length to false, then assert(arg) can never
happen, so the warning is given.
Also note that assert(0), which is what that line reduces to, is *not*
removed for release builds.
It is obvious, however, that the assertion will never be executed anyway.
No it isn't. this:
foo!(A, int)(true);
compiles to the same exact template function instantiation. arg is a
runtime parameter, not determinable at compile-time, and therefore the
compiler must include the branch.
Is there some way around this? (other than compiling without -w)
I can't help but feel what I'm doing isn't right some how.
Use static assert/static if when you expect something that is determined
at compile time to be a certain way. Not only will it be more efficient
code, but if it's *not* compile-time determined, you will get an error
from the compiler.
-Steve
