dyn bounds

[tomerze]

*Note: Syntax feedback is welcomed.

Let's first look at the problem this feature attempts to solve.

For example, I got a type named Cat and a type named Lion both Lion and Cat implement the traits HasName and HasMeow.

I need to create a Vec of references to types that implement both HasName and HasMeow.
As far as I know (and I may be very wrong) this is how you would do that.

//lion is of type Lion , cat is of type Cat.
trait HasBothMeowAndName : HasMeow + HasName {};
impl HasBothMeowAndName for Cat{}
impl HasBothMeowAndName for Lion{}
let vector : Vec<&dyn HasBothMeowAndName> = vec![&lion,&cat];

dyn bounds is a syntax sugar feature attempting to make this ugly code more readable and easier to write.
Simply do
let vector : Vec<&dyn (HasName + HasMeow)> = vec![&lion,&cat];

The code will compile since both Lion and Cat implement the traits HasName and HasMeow.

Of course, you'll be able to use the functions of the traits on every element of the vector.

for entity in vector {
        entity.meow();
        entity.get_name();
}

*The dyn bounds feature isn't limited to the Vec struct.
*You can add more than two traits using the Add operator.
example:
dyn (Trait1 + Trait2 + Trait3 + Trait4)

Readable intuitive and useful.

[SimonSapin]

Is this the same as #2035?

[tomerze]

@SimonSapin seems like it is. different syntax, same idea. issue closed.