On Tue, 11 Sep 2018 18:22:12 -0700
Patrick Smith <pat42sm...@gmail.com> wrote:
> I'm fairly sure there's no way to write Min, but perhaps someone can prove
> me wrong?
Within "Craftsman Go Generics" proposal its trivial:
func Min(a, b T) T {
for type switch {
case T func(T) Less(T) T:
return a.Less(b)
}
if a < b {
return a
}
return b
}
How does it work:
At compile time when compiler sees call to Min(a, b) with
any given type RTA compiler:
1. checks the first (and here single) case of whether T has
Less method defined. If its true, then a Min variant of
Min(a, b __TbyLess) __TbyLess {
return a.Less(b)
}
is instantiated. "__TbyLess" denotes that its an internal compiler
representation and reminds that only single piece/part of code will ever
be produced out of single "for type switch" case.
2. If it does not (have Less method) "for type switch" case does not match
so "it does not exist" in regards to current type check, so now we have
func Min(a, b __TbyOtherMeans) __TbyOtherMeans {
if a < b {
return a
}
return b
}
}
Now if the type is NOT comparable, compiler says to us that we can not
use Min with type RTA. (CGG contracts operate on types, not on artificial
statements).
If RTA type is comparable, compiler makes variant of output code, hopefully
marking it internally for reuse with wide class of base types.
https://github.com/ohir/gonerics
> (With contracts I'm doubly sure it can't be done, as the contract for Min
> would have to permit both Less and <, so then Min(X) would only be allowed
> for types X having both Less and <.)
TC,
--
Wojciech S. Czarnecki
<< ^oo^ >> OHIR-RIPE
--
You received this message because you are subscribed to the Google Groups
"golang-nuts" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to golang-nuts+unsubscr...@googlegroups.com.
For more options, visit https://groups.google.com/d/optout.
