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

Question

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.

Personally I would setup a hash to function references and then use the string as an index to the hash. You then call the function reference with it's parameters. This has the advantage of not allowing the wrong string to call something you don't want to call. The other way is to basically eval the string. Do not do this.

PS don't be lazy and actually type out your whole question, instead of linking to something.