#cast #into #from #conversion

no-std easy-cast

Type conversions which are expected to succeed

11 releases

0.5.2 Dec 22, 2022
0.5.1 Oct 14, 2022
0.5.0 Aug 19, 2022
0.4.4 Apr 12, 2021
0.1.0 Mar 18, 2021

#100 in Rust patterns

Download history 3819/week @ 2023-08-05 4514/week @ 2023-08-12 3721/week @ 2023-08-19 4463/week @ 2023-08-26 4247/week @ 2023-09-02 3507/week @ 2023-09-09 4039/week @ 2023-09-16 4977/week @ 2023-09-23 4352/week @ 2023-09-30 6240/week @ 2023-10-07 5721/week @ 2023-10-14 4936/week @ 2023-10-21 5238/week @ 2023-10-28 5824/week @ 2023-11-04 5672/week @ 2023-11-11 4206/week @ 2023-11-18

21,610 downloads per month
Used in 15 crates (7 directly)


992 lines


Test Status Docs

Type conversion, success expected

This library exists to make fallible numeric type conversions easy, without resorting to the as keyword.

If you are wondering "why not just use as", there are a few reasons:

  • integer conversions may silently truncate or sign-extend which does not preserve value
  • prior to Rust 1.45.0 float-to-int conversions were not fully defined; since this version they use saturating conversion (NaN converts to 0)
  • you want some assurance (at least in debug builds) that the conversion will preserve values correctly

Why might you not want to use this library?

  • You want saturating / truncating / other non-value-preserving conversion
  • You want to convert non-numeric types (From supports a lot more conversions than Conv does)!
  • You want a thoroughly tested library (we're not quite there yet)

Error handling

All traits support two methods:

  • try_* methods return a Result and always fail if the correct conversion is not possible
  • other methods may panic or return incorrect results

In debug builds, methods not returning Result must panic on failure. As with the overflow checks on Rust's standard integer arithmetic, this is considered a tool for finding logic errors. In release builds, these methods are permitted to return defined but incorrect results similar to the as keyword.

If the always_assert feature flag is set, assertions will be turned on in all builds. Some additional feature flags are available for finer-grained control (see Cargo.toml).


Performance is "good enough that it hasn't been a concern".

In debug builds and when always_assert is enabled, the priority is testing but overhead should be small.

In release builds without always_assert, conv* methods should reduce to x as T (with necessary additions for rounding).

no_std support

When the crate's default features are disabled (and std is not enabled) then the library supports no_std. In this case, ConvFloat and CastFloat are only available if the libm optional dependency is enabled.

MSRV and no_std

The Minumum Supported Rust Version is 1.53.0 (IntoIterator for [T; N]).

By default, std support is required. With default features disabled no_std is supported, but the ConvFloat and CastFloat traits are unavailable. Enabling the libm feature will re-enable these traits.

The COPYRIGHT file includes a list of contributors who claim copyright on this project. This list may be incomplete; new contributors may optionally add themselves to this list.

The easy-cast library is published under the terms of the Apache License, Version 2.0. You may obtain a copy of this licence from the LICENSE file or on the following webpage: https://www.apache.org/licenses/LICENSE-2.0