Error code E0747

Generic arguments were not provided in the same order as the corresponding generic parameters are declared, or a type was provided when a constant was expected.

Erroneous code example:

#![allow(unused)]
fn main() {
struct S<'a, T>(&'a T);

type X = S<(), 'static>; // error: the type argument is provided before the
                         // lifetime argument
}

The argument order should be changed to match the parameter declaration order, as in the following:

#![allow(unused)]
fn main() {
struct S<'a, T>(&'a T);

type X = S<'static, ()>; // ok
}

Another erroneous code example:

#![allow(unused)]
fn main() {
struct Foo<const N: usize>;

fn foo() -> Foo<usize> {} // error: type provided when a constant was
                          // expected
}

A constant expression must be provided when a constant generic parameter is declared, not a type, as in the following:

#![allow(unused)]
fn main() {
struct Foo<const N: usize>;

fn foo() -> Foo<3> { Foo }
}