clippy::string_lit_as_bytes: Checks for the as_bytes method called on string literals that contain only ASCII characters

fn f(v: Vec<u8>) {}

f("...".as_bytes().to_owned()); // works
f(b"...".to_owned()); // does not work, because arg is [u8; 3] not Vec<u8>

fn g(r: impl std::io::Read) {}

g("...".as_bytes()); // works
g(b"..."); // does not work

let bstr = "a byte string".as_bytes();

[lints.clippy]
string_lit_as_bytes = "warn"

#![warn(clippy::string_lit_as_bytes)]

cargo clippy -- -W clippy::string-lit-as-bytes

Clippy's own documentation

What it does

Checks for the as_bytes method called on string literals that contain only ASCII characters.

Why is this bad?

Byte string literals (e.g., b"foo") can be used instead. They are shorter but less discoverable than as_bytes().

Known problems

"str".as_bytes() and the suggested replacement of b"str" are not equivalent because they have different types. The former is &[u8] while the latter is &[u8; 3]. That means in general they will have a different set of methods and different trait implementations.

fn f(v: Vec<u8>) {}

f("...".as_bytes().to_owned()); // works
f(b"...".to_owned()); // does not work, because arg is [u8; 3] not Vec<u8>

fn g(r: impl std::io::Read) {}

g("...".as_bytes()); // works
g(b"..."); // does not work

The actual equivalent of "str".as_bytes() with the same type is not b"str" but &b"str"[..], which is a great deal of punctuation and not more readable than a function call.

Example

let bstr = "a byte string".as_bytes();

Use instead:

let bstr = b"a byte string";

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

Related lints

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• significant_drop_tighteningSearches for elements marked with #[clippy::has_significant_drop] that could be early dropped but are in fact dropped at the end of their scopes
• single_option_map`fn` that only maps over argument
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• suspicious_operation_groupingsthis sequence of operators looks suspiciously like a bug
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All 847 Clippy lints · Rust compiler errors · Cargo.toml checker