Error code E0423

An identifier was used like a function name or a value was expected and the identifier exists but it belongs to a different namespace.

Erroneous code example:

#![allow(unused)] fn main() { struct Foo { a: bool }; let f = Foo(); // error: expected function, tuple struct or tuple variant, found `Foo` // `Foo` is a struct name, but this expression uses it like a function name }

Please verify you didn't misspell the name of what you actually wanted to use here. Example:

#![allow(unused)] fn main() { fn Foo() -> u32 { 0 } let f = Foo(); // ok! }

It is common to forget the trailing ! on macro invocations, which would also yield this error:

#![allow(unused)] fn main() { println(""); // error: expected function, tuple struct or tuple variant, // found macro `println` // did you mean `println!(...)`? (notice the trailing `!`) }

Another case where this error is emitted is when a value is expected, but something else is found:

#![allow(unused)] fn main() { pub mod a { pub const I: i32 = 1; } fn h1() -> i32 { a.I //~^ ERROR expected value, found module `a` // did you mean `a::I`? } }