Even with ::from I'm getting expected type parameter A error [duplicate]

Question

Given this function,

fn incr<A: std::ops::AddAssign>(mut foo: A) -> A {
    foo += A::from(1);
    foo
}

I'm getting,

error[E0308]: mismatched types
 --> src/lib.rs:2:20
  |
1 | fn incr<A: std::ops::AddAssign>(mut foo: A) -> A {
  |         - this type parameter
2 |     foo += A::from(1);
  |                    ^ expected type parameter `A`, found integer
  |
  = note: expected type parameter `A`
                       found type `{integer}`
  = help: type parameters must be constrained to match other types
  = note: for more information, visit https://doc.rust-lang.org/book/ch10-02-traits.html#traits-as-parameters

How can I make this work?

Generally you should use into(), this make the error more clear play.rust-lang.org/… or complete form... play.rust-lang.org/… very verbose — Stargateur
– Stargateur, Commented Apr 29, 2020 at 0:37

Shepmaster · Accepted Answer · 2020-04-29 00:55:13Z

2

You need to specify that A has a trait bound that requires that it implements From<u8>:

fn incr<A: std::ops::AddAssign + From<u8> > (mut foo: A) -> A {
    foo += A::from(1);
    foo
}

edited Apr 29, 2020 at 0:55

Shepmaster

439k116 gold badges1.3k silver badges1.5k bronze badges

answered Apr 28, 2020 at 23:50

Evan Carroll

1

Sign up to request clarification or add additional context in comments.

Collectives™ on Stack Overflow

Even with ::from I'm getting expected type parameter A error [duplicate]

1 Answer 1

Comments

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Linked

Related