Rust error E0790: cannot call associated function on trait without specifying the corresponding `impl` type

What it meansYou need to specify a specific implementation of the trait in order to call the method.

What rustc prints

error[E0790]: cannot call associated function on trait without specifying the corresponding `impl` type
  --> main.rs:19:17
   |
 4 |     fn create() -> u32;
   |     ------------------- `Coroutine::create` defined here
...
19 | let cont: u32 = Coroutine::create();
   |                 ^^^^^^^^^^^^^^^^^^^ cannot call associated function of trait
   |
help: use a fully-qualified path to one of the available implementations
   |
19 | let cont: u32 = <Impl as Coroutine>::create();
   |                 ++++++++          +
19 | let cont: u32 = <AnotherImpl as Coroutine>::create();
   |                 +++++++++++++++          +

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.

E0790Types and traits

Activein rustc 1.99.0

8related errors linked below

The compiler team's explanation

You need to specify a specific implementation of the trait in order to call the method.

Erroneous code example:

trait Coroutine {
    fn create() -> u32;
}

struct Impl;

impl Coroutine for Impl {
    fn create() -> u32 { 1 }
}

struct AnotherImpl;

impl Coroutine for AnotherImpl {
    fn create() -> u32 { 2 }
}

let cont: u32 = Coroutine::create();
// error, impossible to choose one of Coroutine trait implementation
// Should it be Impl or AnotherImpl, maybe something else?

This error can be solved by adding type annotations that provide the missing information to the compiler. In this case, the solution is to use a concrete type:

trait Coroutine {
    fn create() -> u32;
}

struct AnotherImpl;

impl Coroutine for AnotherImpl {
    fn create() -> u32 { 2 }
}

let gen1 = AnotherImpl::create();

// if there are multiple methods with same name (different traits)
let gen2 = <AnotherImpl as Coroutine>::create();

From rustc --explain E0790 (1.99.0), part of the Rust project, MIT or Apache-2.0. Official page.

Up next

Often hit nextE0308: mismatched typesA related error from the same family.Read it next →

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Rust error E0790: cannot call associated function on trait without specifying the corresponding `impl` type

What rustc prints

The compiler team's explanation

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