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:

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

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

fn Foo() -> u32 { 0 }

let f = Foo(); // ok!

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

println("");
// error: expected function, tuple struct or tuple variant,
// found macro `println`
// did you mean `println!(...)`? (notice the trailing `!`)

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

pub mod a {
    pub const I: i32 = 1;
}

fn h1() -> i32 {
    a.I
    //~^ ERROR expected value, found module `a`
    // did you mean `a::I`?
}

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