Clippy lints / Pedantic
Clippy lint · Pedantic · checked with Clippy 0.1.99
clippy::struct_excessive_bools: Checks for excessive use of bools in structs
What it meansChecks for excessive use of bools in structs. It is in the pedantic group and off by default.
Does it matter?
Excessive bools in a struct is often a sign that the type is being used to represent a state machine, which is much better implemented as an enum. The reason an enum is better for state machines over structs is that enums more easily forbid invalid states. Structs with too many booleans may benefit from refactoring into multi variant enums for better readability and API.
Stricter lints with some false positives. Off by default; opt in with clippy::pedantic.
How to fix it
Clippy does not fix this one automatically. Change the code by hand:
Flagged
struct S {
is_pending: bool,
is_processing: bool,
is_finished: bool,
}
Write this instead
enum S {
Pending,
Processing,
Finished,
}
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]
struct_excessive_bools = "warn"In code
#![warn(clippy::struct_excessive_bools)]One run
cargo clippy -- -W clippy::struct-excessive-boolsThe [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.
Settings in clippy.toml
max-struct-bools: The maximum number of bool fields a struct can have
Clippy's own documentation
What it does
Checks for excessive use of bools in structs.
Why is this bad?
Excessive bools in a struct is often a sign that the type is being used to represent a state machine, which is much better implemented as an enum.
The reason an enum is better for state machines over structs is that enums more easily forbid invalid states.
Structs with too many booleans may benefit from refactoring into multi variant enums for better readability and API.
Example
struct S {
is_pending: bool,
is_processing: bool,
is_finished: bool,
}
Use instead:
enum S {
Pending,
Processing,
Finished,
}
Configuration
-
max-struct-bools: The maximum number of bool fields a struct can have(default:
3)
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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- stable_sort_primitiveused `sort` on primitive type `i32`
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- string_add_assignyou assigned the result of adding something to this string. Consider using `String::push_str()` instead
- struct_field_namesfield name starts with the struct's name
- transmute_ptr_to_ptrtransmute from a pointer to a pointer
All 847 Clippy lints · Rust compiler errors · Cargo.toml checker
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