Error code E0121
The type placeholder _
was used within a type on an item's signature.
Erroneous code example:
#![allow(unused)] fn main() { fn foo() -> _ { 5 } // error static BAR: _ = "test"; // error }
In those cases, you need to provide the type explicitly:
#![allow(unused)] fn main() { fn foo() -> i32 { 5 } // ok! static BAR: &str = "test"; // ok! }
The type placeholder _
can be used outside item's signature as follows:
#![allow(unused)] fn main() { let x = "a4a".split('4') .collect::<Vec<_>>(); // No need to precise the Vec's generic type. }