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I want to define a method that takes keyword arguments. I would like it to raise when keyword arguments are not provided, and I can code this myself - but ideally I would like to let Ruby do that for me. Also I would like to be able to inspect the freshly defined method using Method#parameters. If I use a shorthand double-splat (like **kwargs) the actual structure I expect is not visible to parameters.
I can of course do this:
define_method(:foo) do | foo:, bar: |
# ...
end
which achieves the desired result:
method(:foo).parameters
# => [[:keyreq, :foo], [:keyreq, :bar]]
but I cannot pass those arguments programmatically, they have to be literally placed in the code. Is there a way I could bypass this?
332
What are keyword arguments? Keyword arguments are a feature in Ruby 2.0 and higher. They're an alternative to positional arguments, and are really similar (conceptually) to passing a hash to a function, but with better and more explicit errors.
define_method is a method defined in Module class which you can use to create methods dynamically. To use define_method , you call it with the name of the new method and a block where the parameters of the block become the parameters of the new method.
One way to invoke a method dynamically in ruby is to send a message to the object. We can send a message to a class either within the class definition itself, or by simply sending it to the class object like you'd send any other message.
You have to use eval to define arguments dynamically (not just keyword arguments), e.g. using class_eval:
class MyClass
name = :foo
args = [:bar, :baz]
class_eval <<-METHOD, __FILE__, __LINE__ + 1
def #{name}(#{args.map { |a| "#{a}:" }.join(', ')}) # def foo(bar:, baz:)
[#{args.join(', ')}] # [bar, baz]
end # end
METHOD
end
MyClass.new.foo(bar: 1, baz: 2)
#=> [1, 2]
MyClass.instance_method(:foo).parameters
#=> [[:keyreq, :bar], [:keyreq, :baz]]
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