Hi everyone,
There is currently a feature whereby custom enum variant discriminants
can be specified:
pub enum Foo {
Bar = 1,
Baz = 2,
Boo = 3,
}
The sole use of this is casting from the enum to an int:
println(fmt!("%d", Bar as int)); // prints 1
This feature currently doesn't really meet people's needs. Chief among
the issues are:
1. Only ints are supported, but many enums want to correspond to
different sizes of types.
2. Only casting *from* an enum value is supported, not casting *to* an
enum value. Casting to an enum value is not supported because this is a
partial operation.
3. There is no way to have multiple values correspond to a single enum
variant.
We could extend the syntax to support these in some way, but I'm
personally leaning toward just moving the machinery into a syntax
extension. You could write something like:
numeric_enum!(Foo : uint {
Bar = 1,
Baz = 2 | 3,
Boo = 4
})
Then the compiler would generate functions like:
Foo::from_uint(uint) -> Result<Foo,()>
Foo::to_uint(self) -> uint
One could also imagine a similar syntax extension for bitfields.
Besides the obvious advantage that it simplifies the language, we can
make the `from_foo` type return a proper Result (or use the condition
system) without building Result into the compiler.
Thoughts?
Patrick
_______________________________________________
Rust-dev mailing list
[email protected]
https://mail.mozilla.org/listinfo/rust-dev
