I agree that overloadable * would be very desirable for smart
pointers. I also really like the interaction with newtypes. Is it
still the plan (from the GC thread) to push all mutability into Cell?
Would that interact with this proposal in any way (e.g. to allow
mutating through * in some cases)?
The method lookup part of it feels too magical. What if both the
pointer and the pointee have a method with the same name? In general,
how can you tell whether you're calling a method on the "pointer" or
the "pointee"? The reason using the dot both for calling methods
directly and for calling them through pointers worked so far is that
pointers didn't have methods. Disambiguating this situation is what
C++ has the -> operator for: would it be so bad to adopt it? With a
simple desugaring to (*foo).bar it would remove the magic, and the
common fields use case would also continue to work with a different
syntax. I'm guessing this is another of those decisions that was
discussed and settled a long time ago. Is there any other language
with universal dot notation where custom smart pointers are common?
On Tue, Jul 30, 2013 at 7:28 AM, Patrick Walton <pwal...@mozilla.com> wrote:
> Currently, newtype structs automatically dereference to the value they
> contain; for example:
>
> struct MyInt(int);
> fn main() {
> let x = MyInt(3);
> printfln("1 + 2 = " + x.to_str()); // prints "1 + 2 = 3"
> }
>
> This behavior is sometimes undesirable, as Brian often points out. Haskell
> allows behavior similar to this to be controlled on an opt-in basis with
> `GeneralizedNewtypeDeriving`.
I think these are subtly different. Rust is automatically unwrapping
the newtype when calling a method on it, while Haskell is
automatically generating requested trait impls based on the ones for
the inner type. But not vice versa: for functions other than those on
derived traits/classes Haskell still requires manual unwrapping, and
Rust doesn't consider the newtype to impl traits just because the
inner type does. Allowing overloads of */-> on newtypes and
GeneralizedNewtypeDeriving would be independently useful features
(just be careful when mixing the latter with associated types).
--
Your ship was destroyed in a monadic eruption.
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