On Friday, 9 March 2018 at 01:22:15 UTC, Mike Franklin wrote:
* binary assignment operators (e.g. +=)
* unary assignment operators (e.g. ++)
* @safe, @nogc, and -betterC compatible
* at least as good code generation as that proposed in the DIP
when optimizations are enabled.
* And should be scalable to data that isn't addressable (e.g.
bitfields). See
https://issues.dlang.org/show_bug.cgi?id=16187
This is the best I've come up with in the current language:
struct S {
int n;
mixin property!("field", "get => this.n", "set => this.n =
set");
}
unittest {
import std.conv : to;
S s;
s.field = 3;
assert(s.field == 3);
s.field += 2;
assert(s.field == 5);
s.field++;
assert(s.field == 6);
assert(s.field.to!string == "6");
}
Sadly, there are issues:
1) Wrong return type:
unittest {
S s;
auto a = s.field;
// Fails - typeof(a) is Property!((get) => this.n, (set) =>
this.n = set)
assert(is(typeof(a) == int));
}
Not a whole lot to do about this. I've pondered writing a DIP on
auto-decaying/rvalue types, which would decay to a different type
the moment they're passed to a function or assigned to a
variable. The feature would probably not be worth the trouble,
though.
2) Noisy syntax:
If I had my druthers, mixin templates would be mixin'd
automatically, and eponymous mixin templates would be a thing.
That would give us this syntax:
struct S {
int n;
property!("get => this.n", "set => this.n = set") field;
}
3) Stringy functions:
The string literal functions are an eyesore, but would require
some compiler work to fix. This fails:
struct S {
int n;
mixin property!("field", get => this.n, set => this.n = set);
}
The reason is there's no 'this' at the point of instantiation,
since we're in the context of the type, not a function where
'this' makes sense. It seems to me this should be fixable, but I
have no idea how much work would be required.
4) 'this' in function bodies
It should be possible to write "get => this.n" as "get => n".
There's no ambiguity as to which 'n' I'm referring to. Filed a
bug:
https://issues.dlang.org/show_bug.cgi?id=18584
Implementation:
https://gist.github.com/Biotronic/5849af011cbe9c7ea05515011d5995bf
--
Simen
