clippy::or_fun_call: Checks for calls to .or(foo(..)), .unwrap_or(foo(..)), .or_insert(foo(..)) etc., and suggests to use .or_else(|| foo(..)), .unwrap_or_else(|| foo(..)), .unwrap_or_default() or .or_default() etc

foo.unwrap_or(String::from("empty"));

foo.unwrap_or_else(|| String::from("empty"));

[lints.clippy]
or_fun_call = "warn"

#![warn(clippy::or_fun_call)]

cargo clippy -- -W clippy::or-fun-call

Clippy's own documentation

What it does

Checks for calls to .or(foo(..)), .unwrap_or(foo(..)), .or_insert(foo(..)) etc., and suggests to use .or_else(|| foo(..)), .unwrap_or_else(|| foo(..)), .unwrap_or_default() or .or_default() etc. instead.

Why is this bad?

The function will always be called. This is only bad if it allocates or does some non-trivial amount of work.

Known problems

If the function has side-effects, not calling it will change the semantic of the program, but you shouldn’t rely on that.

The lint also cannot figure out whether the function you call is actually expensive to call or not.

Example

foo.unwrap_or(String::from("empty"));

Use instead:

foo.unwrap_or_else(|| String::from("empty"));

Configuration

• msrv: The minimum rust version that the project supports. Defaults to the rust-version field in Cargo.toml

  (default: current version)

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

Related lints

• redundant_cloneChecks for a redundant clone() (and its relatives) which clones an owned value that is going to be dropped without further use
• needless_type_castChecks for bindings (constants, statics, or let bindings) that are defined with one numeric type but are consistently cast to a different type in all usages
• non_send_fields_in_send_tyThis lint warns about a Send implementation for a type that contains fields that are not safe to be sent across threads. It tries to detect fields that can cause a soundness issue when sent to another thread (e.g., Rc) while allowing !Send fields that are expected to exist in a Send type, such as raw pointers
• option_if_let_elseLints usage of if let Some(v) =
• path_buf_push_overwritecalling `push` with '/' or '\' (file system root) will overwrite the previous path definition
• read_zero_byte_vecreading zero byte data to `Vec`

All 847 Clippy lints · Rust compiler errors · Cargo.toml checker