On Friday, 13 December 2013 at 12:50:01 UTC, Nicolas Sicard wrote:
On Friday, 13 December 2013 at 12:10:02 UTC, comco wrote:
Imagine a world in which a simple 'if' has the semantics of a
static if, if the condition is evaluable at CT. Is this a
world you would rather live in?
template Fac(int i) {
if (i == 0) { // static if; doesn't introduce scope
enum Fac = 1;
} else {
enum Fac = i * Fac!(i-1);
}
}
// If the condition is not evaluable at CT, the ordinary
runtime if semantics (introducing scope) are used.
Me:
pros: simpler syntax
cons: harder to reason about; I recall Andrei's talk about the
static if proposal to C++: "we don't need _static else_" --
why do we even need 'static' in 'static if' by this reasoning?
What would happen when the condition is sometimes evaluable at
compile time and sometimes not?
void foo(alias a)() {
/* static */ if (a)
int x = 1;
else
int x = 42;
doSomethingWith(x);
}
Multiple versions of the foo function - depending on the caller -
as it is with templates? Static ifs already can produce a
combinatorial explosion of different method implementations :)
At least in the places where declarations are expected and normal
if doesn't make sense: like template/class/struct body, if can be
implicitly static. Now it is implicitly static right after
function / class / template declarations.
class A(T) {
if (is(T : B))
B b;
else
T b;
...
}
