metaprogramming - Dynamic method calling in Ruby

Question

As far as I am aware there are three ways to dynamically call a method in Ruby:

Method 1:

s = SomeObject.new
method = s.method(:dynamic_method)
method.call

Method 2:

s = SomeObject.new
s.send(:dynamic_method)

Method 3:

s = SomeObject.new
eval "s.dynamic_method"

By benchmarking them I have established that Method 1 is by far the fastest, Method 2 is slower, and Method 3 is by far the slowest.

I have also found that .call and .send both allow calling private methods, while eval does not.

So my question is: is there any reason to ever use .send or eval? Why would you not always just use the fastest method? What other differences do these methods of calling dynamic methods have?

Answer 1

is there any reason to ever use send?

call needs a method object, send doesn't:

class Foo
  def method_missing(name)
    "#{name} called"
  end
end

Foo.new.send(:bar)         #=> "bar called"
Foo.new.method(:bar).call  #=> undefined method `bar' for class `Foo' (NameError)

is there any reason to ever use eval?

eval evaluates arbitrary expressions, it's not just for calling a method.

---

Regarding benchmarks, send seems to be faster than method + call:

require 'benchmark'

class Foo
  def bar; end
end

Benchmark.bm(4) do |b|
  b.report("send") { 1_000_000.times { Foo.new.send(:bar) } }
  b.report("call") { 1_000_000.times { Foo.new.method(:bar).call } }
end

Result:

           user     system      total        real
send   0.210000   0.000000   0.210000 (  0.215181)
call   0.740000   0.000000   0.740000 (  0.739262)