CODEWITHSUNDEEP
rubydynamicmetaprogrammingdynamic-programming
freemanoid
freemanoid

Reputation: 14770

Ruby dynamic arguments in dynamically created methods

I have the following kind of method definition:

method_name = :foo
method_arguments = [:bar, :baz]
method_mandatory_arguments = {:quux => true}
method_body = ->{ quux ? bar + baz : bar - baz }

So I want to get a real method. But define_method has no any possibility to define method arguments dynamically. I know another way to use class_eval but I know than defining methods with class_eval is much slower than define_method. How I can effectively archive this?

I did some benchmarks in rails console: 

class Foo; end
n = 100_000

Benchmark.bm do |x|
  x.report('define_method') do
    n.times { |i| Foo.send(:define_method, "method1#{i}", Proc.new { |a, b, c| a + b + c }) }
  end
  x.report('class_eval') do
    n.times { |i| Foo.class_eval %Q{ def method2#{i}(a, b, c); a + b + c; end } }
  end
end

So I've got the following results:

                user       system     total      real
define_method  0.750000   0.040000   0.790000 (  0.782988)
class_eval     9.510000   0.070000   9.580000 (  9.580577)

Upvotes: 4

Views: 2829

Answers (1)

Simon Perepelitsa
Simon Perepelitsa

Reputation: 20639

There is no simple way to implement what you are asking using either class_eval or define_method. Since method_body is a lambda it can only access local variables defined right before it.

method_body = ->{ quux ? bar + baz : bar - baz }
quux = true
method_body.call # undefined local variable or method ‘quux’

quux = true
method_body = ->{ quux ? bar + baz : bar - baz }
method_body.call # undefined local variable or method ‘bar’

I would suggest you to revise your requirements. If your method body should be a lambda, define all arguments for it. Then this is a natural fit for define_method:

method_body = ->(quux, bar = 0, baz = 0){ quux ? bar + baz : bar - baz }
define_method(method_name, &method_body)

If your method body can be a string, eval is the only option:

method_body = "quux ? bar + baz : bar - baz"
eval <<RUBY
def #{method_name} #{arguments}
  #{method_body}
end
RUBY

Upvotes: 3

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