gistfile1.rb

# This code is under BSD 3-clause license
# Author: Stefan Rusterholz <stefan.rusterholz@gmail.com> (aka apeiros)

module Kernel
  ValidLocalVariableName = /\A[a-z_]\w*\z/

  # Dynamically define a bunch of local variables from a hash.
  # Overrides existing local variables.
  #
  # IMPORTANT: This is an anti-pattern. Think thrice before using this. It
  # almost always means you're doing it wrong and should use a Hash instead.
  #
  # Arguments:
  #   binding:     The binding the variables should appear in, usually this is
  #                the current binding which you get via Kernel#binding
  #   variables:   A Hash containing the variable names and their values. The
  #                keys must be Symbols. The values can be any object.
  #   valid_names: Optional. An array with valid local variable names.
  #
  # Example:
  #   extract(binding, :foo => 1, :bar => 2)
  #   foo # => 1
  #   bar # => 2
  #   extract(binding, :foo => 3, :bar => 4)
  #   foo # => 3
  #   bar # => 4
  #
  # Also see Kernel#safe_extract
  #
  def extract(binding, variables, valid_names=nil)

    # Verify against provided variable names
    if valid_names && !(variables.keys-valid_names).empty? then
      raise ArgumentError,
            "Contains invalid names #{(variables.keys-valid_names).join(', ')}"
    end

    # Verify that all names are really names to prevent code injection
    # only do it if the user didn't provide a list with valid names
    unless valid_names || variables.keys.all? { |name| name.to_s =~ ValidLocalVariableName }
      raise ArgumentError, "Contains invalid identifiers"
    end

    # Deposit the data somewhere threadsafe without corrupting the namespace
    Thread.current[:__extract__] = variables

    # Assign the lvars from our deposit
    code = "#{variables.keys.join(', ')} = Thread.current[:__extract__]." \
           "values_at(:#{variables.keys.join(', :')})"
    eval(code, binding)

    # Clean up
    Thread.current[:__extract__] = nil # no `Thread#delete`? odd...

    nil
  end
  module_function :extract

  # Dynamically define a bunch of local variables from a hash.
  # Will only set previously undefined local variables.
  #
  # IMPORTANT: This is an anti-pattern. Think thrice before using this. It
  # almost always means you're doing it wrong and should use a Hash instead.
  #
  # Arguments:
  #   binding:     The binding the variables should appear in, usually this is
  #                the current binding which you get via Kernel#binding
  #   variables:   A Hash containing the variable names and their values. The
  #                keys must be Symbols. The values can be any object.
  #   valid_names: Optional. An array with valid local variable names.
  #
  # Example:
  #   safe_extract(binding, :foo => 1, :bar => 2)
  #   foo # => 1
  #   bar # => 2
  #   safe_extract(binding, :foo => 3, :bar => 4)
  #   foo # => 1
  #   bar # => 2
  #
  # Also see Kernel#extract
  #
  def safe_extract(binding, variables, valid_names=nil)

    # Verify against provided variable names
    if valid_names && !(variables.keys-valid_names).empty? then
      raise ArgumentError,
            "Contains invalid names #{(variables.keys-valid_names).join(', ')}"
    end

    # Verify that all names are really names to prevent code injection
    # only do it if the user didn't provide a list with valid names
    unless valid_names || variables.keys.all? { |name| name.to_s =~ ValidLocalVariableName }
      raise ArgumentError, "Contains invalid identifiers"
    end

    # Deposit the data somewhere threadsafe without corrupting the namespace
    Thread.current[:__extract__] = variables

    # Assign the lvars from our deposit
    variables.each_key do |name|
      eval("unless defined?(#{name}) == 'local-variable'; #{name} = Thread.current[:__extract__][:#{name}]; end", binding)
    end

    # Clean up
    Thread.current[:__extract__] = nil # no `Thread#delete`? odd...

    nil
  end
  module_function :safe_extract
end