Performance-ConstantRegexp.md

Pattern: Regexp with dynamic components that are all constants

Issue: -

Description

Finds regular expressions with dynamic components that are all constants.

Ruby allocates a new Regexp object every time it executes a code containing such a regular expression. It is more efficient to extract it into a constant or add an /o option to perform #{} interpolation only once and reuse that Regexp object.

Examples

# bad
def tokens(pattern)
  pattern.scan(TOKEN).reject { |token| token.match?(/\A#{SEPARATORS}\Z/) }
end

# good
ALL_SEPARATORS = /\A#{SEPARATORS}\Z/
def tokens(pattern)
  pattern.scan(TOKEN).reject { |token| token.match?(ALL_SEPARATORS) }
end

# good
def tokens(pattern)
  pattern.scan(TOKEN).reject { |token| token.match?(/\A#{SEPARATORS}\Z/o) }
end

Further Reading

• RuboCop - Performance/ConstantRegexp