Rust error E0191: the value of the associated type `Bar` in `Trait` must be specified

What rustc prints

error[E0191]: the value of the associated type `Bar` in `Trait` must be specified
 --> main.rs:5:16
  |
2 |     type Bar;
  |     -------- `Bar` defined here
...
5 | type Foo = dyn Trait; // error: the value of the associated type `Bar` (from
  |                ^^^^^
  |
help: specify the associated type
  |
5 | type Foo = dyn Trait<Bar = /* Type */>; // error: the value of the associated type `Bar` (from
  |                     ++++++++++++++++++

Real output of rustc 1.99.0 compiling the official example below (2021 edition). Your names and line numbers will differ; the first line is the part to match.

trait Trait {
    type Bar;
}

type Foo = dyn Trait; // error: the value of the associated type `Bar` (from
                      //        the trait `Trait`) must be specified

trait Trait {
    type Bar;
}

type Foo = dyn Trait<Bar=i32>; // ok!

Related errors

• E0308mismatched types
• E0277the trait bound is not satisfied
• E0599no method named X found in the current scope
• E0433failed to resolve
• E0185method `foo` has a `&self` declaration in the impl, but not in the trait
• E0186method `foo` has a `&self` declaration in the trait, but not in the impl
• E0197inherent impls cannot be unsafe
• E0198negative impls cannot be unsafe

All 518 Rust error codes · Rust crate data · Glossary