clippy::as_conversions: Checks for usage of as conversions. Note that this lint is specialized in linting every single use of as regardless of whether good alternatives exist or not

let a: u32;
...
f(a as u16);

f(a.try_into()?);

// or

f(a.try_into().expect("Unexpected u16 overflow in f"));

[lints.clippy]
as_conversions = "warn"

#![warn(clippy::as_conversions)]

cargo clippy -- -W clippy::as-conversions

Clippy's own documentation

What it does

Checks for usage of as conversions.

Note that this lint is specialized in linting every single use of as regardless of whether good alternatives exist or not. If you want more precise lints for as, please consider using these separate lints:

• clippy::cast_lossless
• clippy::cast_possible_truncation
• clippy::cast_possible_wrap
• clippy::cast_precision_loss
• clippy::cast_sign_loss
• clippy::char_lit_as_u8
• clippy::fn_to_numeric_cast
• clippy::fn_to_numeric_cast_with_truncation
• clippy::ptr_as_ptr
• clippy::unnecessary_cast
• invalid_reference_casting

There is a good explanation the reason why this lint should work in this way and how it is useful in this issue.

Why restrict this?

as conversions will perform many kinds of conversions, including silently lossy conversions and dangerous coercions. There are cases when it makes sense to use as, so the lint is Allow by default.

Example

let a: u32;
...
f(a as u16);

Use instead:

f(a.try_into()?);

// or

f(a.try_into().expect("Unexpected u16 overflow in f"));

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

Related lints

• unwrap_usedChecks for .unwrap() or .unwrap_err() calls on Results and .unwrap() call on Options
• module_name_repetitionsDetects public item names that are prefixed or suffixed by the containing public module’s name
• expect_usedChecks for .expect() or .expect_err() calls on Results and .expect() call on Options
• allow_attributes_without_reason`allow` attribute without specifying a reason
• arbitrary_source_item_orderingincorrect ordering of items (must be alphabetically ordered)
• arithmetic_side_effectsarithmetic operation that can potentially result in unexpected side-effects
• as_pointer_underscoreusing inferred pointer cast
• as_underscoreusing `as _` conversion
• assertions_on_result_statesChecks for assert!(r.is_ok()) or assert!(r.is_err()) calls

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