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

Question

How can I do what they are talking about here, but in Ruby?

How would you do the function on an object? and how would you do a global function (see jetxee's answer on the post mentioned)?

EXAMPLE CODE:

event_name = "load"

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

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

#something here to see that event_name = "load" and run load()

UPDATE: How do you get to the global methods? or my global functions?

I tried this additional line

puts methods

and load and row_change where not listed.

mu is too short · Accepted Answer · 2018-11-21 21:35:47Z

270

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:

edited Nov 21, 2018 at 21:35

mu is too short

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answered Sep 10, 2009 at 20:17

Colin Gravill

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11 Comments

BuddyJoe Over a year ago

+1 That works. This may be a dumb follow up ... but how come I can't find the word send in the Ruby source at - C:\ruby\lib\ruby\1.8\fileutils.rb? Thought I would find the send function in there.

BuddyJoe Over a year ago

I was curious to what it was doing under the hood.

Colin Gravill Over a year ago

It's defined on object - ruby-doc.org/core/classes/Object.html#M000332 I picked a random function for interest value.

BuddyJoe Over a year ago

Interesting because before I read your answer twice, and fully grok'd it I ran the FileUtils.send("load") and it ran my function. so if I understand this correctly by creating functions in "global" am I adding the methods onto the root object? or not?

Colin Gravill Over a year ago

Good on you for looking stuff up in the source! :)

|

Community · Accepted Answer · 2020-06-20 09:12:55Z

45

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.

edited Jun 20, 2020 at 9:12

CommunityBot

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answered Aug 8, 2015 at 13:09

cwd

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4 Comments

thesecretmaster Over a year ago

I was just finding this, and I noticed something that wasn't covered. What would I do if I wanted to do Class.send("classVariable") = 5? That throws an error. Is there any way around that? The same thing is true for using Class.method("classVariable").call() = 5

Aleem Over a year ago

if you want to send some argument with send call use something like this ClassName.send("method_name", arg1, arg2)

Joshua Pinter Over a year ago

Shouldn't your benchmark for call include instantiating the method object (m.test.method(:length)) to accurately represent it's true time? When using call you're likely going to instantiate the method object every time.

Joshua Pinter Over a year ago

Blog post link is dead, btw.

Geo · Accepted Answer · 2009-09-10 20:18:56Z

34

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.

answered Sep 10, 2009 at 20:18

Geo

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2 Comments

user1735921 Over a year ago

meth = a.method? isn't this call the function already? what if the method returns something?

Joshua Pinter Over a year ago

FYI for when the method doesn't exist: "my_string".method('blah') #=> NameError: undefined method blah' for class String'

dlamblin · Accepted Answer · 2009-09-10 20:16:03Z

3

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.

answered Sep 10, 2009 at 20:16

dlamblin

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1 Comment

BuddyJoe Over a year ago

Sorry. I'll copy some of the wording and translate to make it Ruby specific. +1

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

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