Calling a Method From a String With the Method's Name in Ruby

To call functions directly on an object

a = [2, 2, 3]
a.send("length")
# or
a.public_send("length")

which returns 3 as expected

or for a module function

FileUtils.send('pwd')
# or
FileUtils.public_send(:pwd)

and a locally defined method

def load()
    puts "load() function was executed."
end

send('load')
# or
public_send('load')

Documentation:

• Object#public_send
• Object#send

Three Ways: send / call / eval - and their Benchmarks

Typical invocation (for reference):

s= "hi man"
s.length #=> 6

Using send

s.send(:length) #=> 6

Using call

method_object = s.method(:length) 
p method_object.call #=> 6

Using eval

eval "s.length" #=> 6

 

Benchmarks

require "benchmark" 
test = "hi man" 
m = test.method(:length) 
n = 100000 
Benchmark.bmbm {|x| 
  x.report("call") { n.times { m.call } } 
  x.report("send") { n.times { test.send(:length) } } 
  x.report("eval") { n.times { eval "test.length" } } 
} 

...as you can see, instantiating a method object is the fastest dynamic way in calling a method, also notice how slow using eval is.

#######################################
#####   The results
#######################################
#Rehearsal ----------------------------------------
#call   0.050000   0.020000   0.070000 (  0.077915)
#send   0.080000   0.000000   0.080000 (  0.086071)
#eval   0.360000   0.040000   0.400000 (  0.405647)
#------------------------------- total: 0.550000sec

#          user     system      total        real
#call   0.050000   0.020000   0.070000 (  0.072041)
#send   0.070000   0.000000   0.070000 (  0.077674)
#eval   0.370000   0.020000   0.390000 (  0.399442)

Credit goes to this blog post which elaborates a bit more on the three methods and also shows how to check if the methods exist.

Use this:

> a = "my_string"
> meth = a.method("size")
> meth.call() # call the size method
=> 9

Simple, right?

As for the global, I think the Ruby way would be to search it using the methods method.