module ActiveSupport::Inflector

def underscore(camel_cased_word)

Experimental RBS support (using type sampling data from the type_fusion project). 

def underscore: (String camel_cased_word) -> untyped

This signature was generated using 1 sample from 1 application.

camelize(underscore('SSLError')) # => "SslError"

#camelize, though there are cases where that does not hold:
As a rule of thumb you can think of +underscore+ as the inverse of

underscore('ActiveModel::Errors') # => "active_model/errors"
underscore('ActiveModel') # => "active_model"

Changes '::' to '/' to convert namespaces to paths.

Makes an underscored, lowercase form from the expression in the string. 
def underscore(camel_cased_word)
  return camel_cased_word.to_s unless /[A-Z-]|::/.match?(camel_cased_word)
  word = camel_cased_word.to_s.gsub("::", "/")
  word.gsub!(inflections.acronyms_underscore_regex) { "#{$1 && '_' }#{$2.downcase}" }
  word.gsub!(/([A-Z])(?=[A-Z][a-z])|([a-z\d])(?=[A-Z])/) { ($1 || $2) << "_" }
  word.tr!("-", "_")
  word.downcase!
  word
end