ParameterValidator is a mixin module providing parameter validation for functions and methods that employ Ruby’s "keyword arguments" implemention.

To use it in a class:


  require 'parmvalid'

  class Demo
    include ParameterValidator

    def initialize( args )
      validate_and_instantiate_parameters( args,
        { :name=>REQUIRED, :date=>, :location=nil, :memo=>REQUIRED } )

      p @name
      p @date
      p @location
      p @memo

  d = :name=>"Jamis", :memo=>"Some memo" )

Author: Jamis Buck (

Classes and Modules
Class ParameterValidator::InvalidParameterException
Class ParameterValidator::MissingParameterException
Public Instance methods
instantiate_parameters( parms )

For each key in the given hash, create an identically-named instance variable and set its value to the value of the given key.

     # File lib/parmvalid.rb, line 115
115:   def instantiate_parameters( parms )
116:     parms.each_pair do |key, value|
117:       eval "@#{key} = value"
118:     end
119:   end
set_parameters( parms )

For each key in the given hash, assign its value to an identically-named setter in the current class.

     # File lib/parmvalid.rb, line 123
123:   def set_parameters( parms )
124:     parms.each_pair do |key, value|
125:       eval "self.#{key} = value"
126:     end
127:   end
validate_and_instantiate_parameters( actual_parms, valid_parms )

Validate and instantiate the given parameters by calling both validate_parameters and instantiate_parameters. Return the hash of all parameters.

     # File lib/parmvalid.rb, line 131
131:   def validate_and_instantiate_parameters( actual_parms, valid_parms )
132:     parms = validate_parameters( actual_parms, valid_parms )
133:     instantiate_parameters( parms )
134:     parms
135:   end
validate_and_set_parameters( actual_parms, valid_parms )

Validate and set the given parameters by calling both validate_parameters and set_parameters. Return the hash of all parameters.

     # File lib/parmvalid.rb, line 139
139:   def validate_and_set_parameters( actual_parms, valid_parms )
140:     parms = validate_parameters( actual_parms, valid_parms )
141:     set_parameters( parms )
142:     parms
143:   end
validate_parameters( actual_parms, valid_parms )

Validates a hash of actual parameters (as created by Ruby’s pseudo-"keyword arguments" feature) against a list of valid parameters.


  • actual_parms: the hash of actual parameters that were given by Ruby’s pseudo-"keyword arguments" feature.
  • valid_parameters: the hash of valid parameters, where the key for each entry in the hash is a symbol naming the acceptable parameter, and the value is the default value for that parameter. If the default value for any entry is the constant REQUIRED, then the parameter must not be absent from the actual_parms hash.

Returns: a hash of all parameters, together with either the actual value that was passed in, or (in the case of optional parameters that were not passed in) the default value.

     # File lib/parmvalid.rb, line 86
 86:   def validate_parameters( actual_parms, valid_parms )
 87:     parms =
 89:     # set the default values
 90:     valid_parms.each_pair do |key,value|
 91:       next if value == REQUIRED
 92:       parms[ key ] = value
 93:     end
 95:     # set the actual values
 96:     actual_parms.each_pair do |key,value|
 97:       if not valid_parms.include? key
 98:         raise InvalidParameterException, "'#{key}' is invalid"
 99:       end
100:       parms[ key ] = value
101:     end
103:     # check required parameters
104:     valid_parms.each_pair do |key,value|
105:       if value==REQUIRED and not parms.include? key
106:         raise MissingParameterException, "'#{key}' is required"
107:       end
108:     end
110:     parms
111:   end