Bug: 156793009

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  1. dd54769 Merge "Migrate to cargo_embargo." into main am: e8a05f8b22 am: f6096561f6 am: 4451b85dc0 by Treehugger Robot · 4 months ago emu-34-2-dev main master
  2. 4451b85 Merge "Migrate to cargo_embargo." into main am: e8a05f8b22 am: f6096561f6 by Treehugger Robot · 4 months ago
  3. f609656 Merge "Migrate to cargo_embargo." into main am: e8a05f8b22 by Treehugger Robot · 4 months ago
  4. e8a05f8 Merge "Migrate to cargo_embargo." into main by Treehugger Robot · 4 months ago emu-34-3-release
  5. 589c2a9 Migrate to cargo_embargo. by Andrew Walbran · 4 months ago

heck is a case conversion library

I specifically requested the opposite of this.

This library exists to provide case conversion between common cases like CamelCase and snake_case. It is intended to be unicode aware, internally consistent, and reasonably well performing.

Definition of a word boundary

Word boundaries are defined as the “unicode words” defined in the unicode_segmentation library, as well as within those words in this manner:

  1. All underscore characters are considered word boundaries.
  2. If an uppercase character is followed by lowercase letters, a word boundary is considered to be just prior to that uppercase character.
  3. If multiple uppercase characters are consecutive, they are considered to be within a single word, except that the last will be part of the next word if it is followed by lowercase characters (see rule 2).

That is, “HelloWorld” is segmented Hello|World whereas “XMLHttpRequest” is segmented XML|Http|Request.

Characters not within words (such as spaces, punctuations, and underscores) are not included in the output string except as they are a part of the case being converted to. Multiple adjacent word boundaries (such as a series of underscores) are folded into one. (“hello__world” in snake case is therefore “hello_world”, not the exact same string). Leading or trailing word boundary indicators are dropped, except insofar as CamelCase capitalizes the first word.

Cases contained in this library:

  1. UpperCamelCase
  2. lowerCamelCase
  3. snake_case
  4. kebab-case
  6. Title Case
  8. Train-Case


PRs of additional well-established cases welcome.

This library is a little bit opinionated (dropping punctuation, for example). If that doesn't fit your use case, I hope there is another crate that does. I would prefer not to receive PRs to make this behavior more configurable.

Bug reports & fixes always welcome. :-)


The minimum supported Rust version for this crate is 1.32.0. This may change in minor or patch releases, but we probably won't ever require a very recent version. If you would like to have a stronger guarantee than that, please open an issue.


heck is distributed under the terms of both the MIT license and the Apache License (Version 2.0).