Clippy lints / Complexity
Clippy lint · Complexity · checked with Clippy 0.1.99
clippy::extra_unused_type_parameters: Checks for type parameters in generics that are never used anywhere else
What it meansChecks for type parameters in generics that are never used anywhere else. It is in the complexity group and warns by default.
Does it matter?
Functions cannot infer the value of unused type parameters; therefore, calling them requires using a turbofish, which serves no purpose but to satisfy the compiler.
Code that does something simple in a complicated way. Warns by default.
How to fix it
Clippy does not fix this one automatically (its suggestion may change behaviour, so it only shows it). Change the code by hand:
Flagged
fn unused_ty<T>(x: u8) {
// ..
}
Write this instead
fn no_unused_ty(x: u8) {
// ..
}
Turn it off, or on
Allow it where it does not fit your code, as narrowly as you can:
On one item
#[allow(clippy::extra_unused_type_parameters)]
fn my_function() { /* ... */ }Whole crate (Cargo.toml)
[lints.clippy]
extra_unused_type_parameters = "allow"One run
cargo clippy -- -A clippy::extra-unused-type-parametersThe [lints] table needs Rust 1.74 or newer. In a workspace, put it under [workspace.lints.clippy] and add [lints] workspace = true to each member.
Clippy's own documentation
What it does
Checks for type parameters in generics that are never used anywhere else.
Why is this bad?
Functions cannot infer the value of unused type parameters; therefore, calling them requires using a turbofish, which serves no purpose but to satisfy the compiler.
Example
fn unused_ty<T>(x: u8) {
// ..
}
Use instead:
fn no_unused_ty(x: u8) {
// ..
}
From the Clippy lint list (0.1.99), part of the Rust project, MIT or Apache-2.0. Official entry.
Related lints
- too_many_argumentsChecks for functions with too many parameters
- clone_on_copyusing `clone` on type `u64` which implements the `Copy` trait
- type_complexityChecks for types used in structs, parameters and let declarations above a certain complexity threshold
- explicit_counter_loopChecks for loops over slices with an explicit counter and suggests the use of .enumerate()
- explicit_writeChecks for usage of write!() / writeln()! which can be replaced with (e)print!() / (e)println!()
- extra_unused_lifetimesthis lifetime isn't used in the function definition
- filter_map_identityChecks for usage of filter_map(|x| x)
- filter_nextChecks for usage of _.filter(_).next()
- flat_map_identityChecks for usage of flat_map(|x| x)
All 847 Clippy lints · Rust compiler errors · Cargo.toml checker
Up next
Related lintclippy::too_many_argumentsChecks for functions with too many parametersRead it next →Did this answer your question?