Created
October 29, 2014 16:08
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module Yaks | |
# State monad-ish thing. | |
# | |
# Generate a DSL syntax for immutable classes. | |
# | |
# @example | |
# | |
# # This code | |
# Control.create(:search) | |
# .method("POST") | |
# .href("/search") | |
# | |
# # Can be written as | |
# StatefulBuilder.new(Control, [:method, :href]).create(:search) do | |
# method "POST" | |
# href "/search" | |
# end | |
# | |
class StatefulBuilder < BasicObject | |
def create(*args, &block) | |
@state = @klass.create(*args) | |
instance_eval(&block) | |
@state | |
end | |
def initialize(klass, methods) | |
@klass = klass | |
StatefulMethods.new(methods).send(:extend_object, self) | |
end | |
def validate_state(method_name, args) | |
unless @state.is_a?(@klass) | |
::Kernel.raise( | |
::Yaks::IllegalState, | |
"#{@klass}##{method_name}(#{args.map(&:inspect).join(', ')}) "\ | |
"returned #{@state.inspect}. Expected instance of #{@klass}" | |
) | |
end | |
end | |
class StatefulMethods < ::Module | |
def initialize(methods) | |
methods.each { |name| define_stateful_method(name) } | |
end | |
def define_stateful_method(method_name) | |
define_method method_name do |*args, &block| | |
@state = @state.public_send(method_name, *args, &block) | |
validate_state(method_name, args) | |
end | |
end | |
end | |
end | |
end |
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