wolfendale / scalacheck-gen-regexp   1.1.0

MIT License GitHub

A library for creating Scalacheck generators from regular expressions

Scala versions: 3.x 2.13 2.12 2.11


A library for creating scalacheck generators from regular expressions

Cross-built for Scala 2.12/2.13/3.1/3.2


In your build.sbt

libraryDependencies += "io.github.wolfendale" %% "scalacheck-gen-regexp" % "[VERSION]"
Quick start
import wolfendale.scalacheck.regexp.RegexpGen

val generator: Gen[String] = RegexpGen.from("[1-9]\\d?(,\\d{3})+")
Supported syntax
Feature Example Notes
Literals a, \\w, 7 Literals are transformed into constant generators
Character Classes [abc], [^abc], [a-zA-Z0-9] Character classes are transformed with Gen.oneOf
Default Classes \w, \d, \S, . These are treated as predefined character classes
Quantifiers a?, b+, c*, d{3}, e{4,5}, f{5,} These use Gen.listOfN to create sized lists of the preceding term
Groups (abc), (?:def) Backreferences are not supported, groups can only be used for grouping terms
Alternates a|b|c, a(b|c)d Alternates are also transformed with Gen.oneOf
Boundaries ^, $, \b Although these will be parsed they do not modify the generator output
Unsupported syntax
Feature Example Notes
Backreferences ([ab]\1) With the current implementation there's no simple way to do this, definitely in consideration for a future release
Octal / Hex / Special Literals \012, \xF1, \p{Lower} Most of these should be simple to implement but I wanted to get an initial release created first
Character Class Intersection [a&&[b]], [a[b]] Difficult to implement currently but not impossible, definite consideration for a future release
Tips for usage
  • In order to represent any character, RegexpGen#from takes an implicit Arbitrary[Char]. There is a default instance provided by scalacheck however for most uses you probably want to provide your own.

  • If you use the + or * quantifiers you'll end up getting huge variance in string sizes. If this isn't what you want, consider bounding the lengths of certain string segments with the {min,max} quantifier.

  • Negated character classes / default classes are implemented by generating an arbitrary Char within certain bounds via suchThat, because of this you can end up throwing away a lot of cases and in certain circumstances your tests may fail. Try to refactor out negative cases.

  • In character classes each option is given equal weighting. If you'd prefer to weight a particular entry you can add it multiple times, this is made easier with string interpolation: s"[${"a-z"*5}\s]". In the example case the generator is 5 times more likely to generate an alpha character than a space.