On 3/23/12 1:48 PM, H. S. Teoh wrote:
How do we check at compile time whether the hash function resolves to
the same entity?
int fun(T)(T x) {
return 42;
}
void main() {
static assert(&fun!int != &fun!double);
}
This actually reveals a compiler bug:
Assertion failed: (d->purity != PUREfwdref), function typeMerge, file
cast.c, line 1909.
A cast would be needed anyway because they have different types, too.
Anyway upon more thinking maybe this is too restrictive a rule. It won't
catch e.g. functions that are, in fact, identical, but come from
distinct instantiations.
So perhaps you need some conservative approximation, i.e. look if the
two types are qualified versions of the same type and then assume they
hash the same.
To include int and double correctly, we'd amend the second rule as
follows. If typeof(x) converts implicitly to typeof(k), then use
hash(cast(typeof(k)) x) instead of hash(x). This makes it possible
to look up for an int in a hash of doubles, but not vice versa,
which is great.
OK.
These two are sufficient for lookup. For store, we also need the
third rule, which is to!(typeof(k))(x) must compile and run.
[...]
Isn't this already required by the hash lookup? Or is casting different
from to!X, in which case it might be messy to import the relevant parts
of phobos into druntime. :-/
Casting is very different from to, and useless for your purposes. You
must use to.
Andrei
