Crate heck

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heck is a case conversion library.

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. CamelCase
  2. snake_case
  3. kebab-case
  5. mixedCase
  6. Title Case


  • This trait defines a camel case conversion.
  • This trait defines a kebab case conversion.
  • This trait defines a mixed case conversion.
  • This trait defines a shouty snake case conversion.
  • Oh heck, ShoutySnekCase is an alias for ShoutySnakeCase. See ShoutySnakeCase for more documentation.
  • This trait defines a camel case conversion.
  • Oh heck, SnekCase is an alias for SnakeCase. See SnakeCase for more documentation.
  • This trait defines a title case conversion.