Clippy lint · Restriction · checked with Clippy 0.1.99

clippy::redundant_type_annotations: redundant type annotation

What it meansWarns about needless / redundant type annotations. It is in the restriction group and off by default.

What you see

warning: redundant type annotation
 --> main.rs:3:1
  |
3 | let foo: String = String::new();
  | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  |
  = help: for further information visit https://rust-lang.github.io/rust-clippy/stable/index.html#redundant_type_annotations
  = note: requested on the command line with `-W clippy::redundant-type-annotations`

Real output of Clippy 0.1.99 (Rust 1.99) on the example below. Names and line numbers in yours will differ.

Does it matter?

Code without type annotations is shorter and in most cases more idiomatic and easier to modify.

Lints that forbid language features for specific codebases (no unwrap, no indexing...). Off by default; pick them one by one, never the whole group.

How to fix it

Clippy does not fix this one automatically. Change the code by hand:

Flagged

let foo: String = String::new();

Write this instead

let foo = String::new();

Turn it off, or on

It is off by default. To use it, set it to warn or deny:

Whole crate (Cargo.toml)

[lints.clippy]
redundant_type_annotations = "warn"

In code

#![warn(clippy::redundant_type_annotations)]

One run

cargo clippy -- -W clippy::redundant-type-annotations

The [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.

Restrictiongroup

allowdefault level

nofixed by cargo clippy --fix

1.72.0added in Rust

Clippy's own documentation

What it does

Warns about needless / redundant type annotations.

Why restrict this?

Code without type annotations is shorter and in most cases more idiomatic and easier to modify.

Limitations

This lint doesn’t support:

Generics
Refs returned from anything else than a MethodCall
Complex types (tuples, arrays, etc…)
Path to anything else than a primitive type.

Example

let foo: String = String::new();

Use instead:

let foo = String::new();

From the Clippy lint list (0.1.99), part of the Rust project, MIT or Apache-2.0. Official entry.

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