# Make a symbol represent a method? **URL:** \ **Category:** Ruby\ **Created:** [December 2, 2005, 8:11pm UTC](https://www.ruby-forum.com/t/make-a-symbol-represent-a-method/49337 "2005-12-02T20:11:56Z")\ **Posts on this page:** 8\ **Page:** 1
**Author:** ![chris.irish](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/4bbf92/32.png) [@chris.irish](https://www.ruby-forum.com/u/chris.irish)\ **Post date:** [December 2, 2005, 8:11pm UTC](https://www.ruby-forum.com/t/make-a-symbol-represent-a-method/49337/1 "2005-12-02T20:11:56Z")
I just read a FAQ page online about Ruby symbols and someone mentions this Also, the entirely realistic reasoning for using symbols: If you are going to refer to a method name, use a symbol. Because by defining the method, the symbol exists anyway. Can someone show me an example of this? Is this referring to the method of a class? ---
**Author:** ![chris.irish](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/4bbf92/32.png) [@chris.irish](https://www.ruby-forum.com/u/chris.irish)\ **Post date:** [December 2, 2005, 8:36pm UTC](https://www.ruby-forum.com/t/make-a-symbol-represent-a-method/49337/2 "2005-12-02T20:36:17Z")
Chris I.: > Also, the entirely realistic reasoning for using symbols: If you are going > to refer to a method name, use a symbol. Because by defining the method, > the symbol exists anyway. > > Can someone show me an example of this? Is this referring to the method > of a class? irb\> def my\_cool\_method; end =\> nil irb\> Symbol.all\_symbols.collect { |s| s.to\_s }.grep /cool/ =\> [“my\_cool\_method”] Malte ---
**Author:** ![chris.irish](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/4bbf92/32.png) [@chris.irish](https://www.ruby-forum.com/u/chris.irish)\ **Post date:** [December 2, 2005, 9:53pm UTC](https://www.ruby-forum.com/t/make-a-symbol-represent-a-method/49337/3 "2005-12-02T21:53:56Z")
On Dec 2, 2005, at 2:38 PM, Chris I. wrote: > One more thing, Can I use the symbol to call a method and pass > arguments to it? Or is it just a reference to the methods name so > that’s not possible? You’re misunderstanding what a Symbol is. A Symbol is is just an immutable String for Ruby. A simple data type. One use for Symbols is to reference a method by name: send(:method\_name) You could also use a String for this though: send(“method\_name”) And you may want to use Symbols for something completely different. I generally use them for keys to my internal Hashes: @parsers = { :leading\_fields =\> Parser.new, :row =\> Parser.new, :line\_endings =\> Parser.new } To answer your question, a little indirectly, yes, send() allows you to pass arguments to the function: send(:method\_name, arg\_1, arg\_2, …) Hope that helps. James Edward G. II ---
**Author:** ![chris.irish](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/4bbf92/32.png) [@chris.irish](https://www.ruby-forum.com/u/chris.irish)\ **Post date:** [December 2, 2005, 9:53pm UTC](https://www.ruby-forum.com/t/make-a-symbol-represent-a-method/49337/4 "2005-12-02T21:53:56Z")
On 12/2/05, Chris I. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > K… I get it > One more thing, Can I use the symbol to call a method and pass arguments > to it? Or is it just a reference to the methods name so that’s not > possible? Sure thing. The symbol is not a reference to the method at all. What the symbol is is a _key_ into the objects method table, the value corresponding to that key is the reference to the Method object. I can use a symbol (it’ll “auto-vivify”, for lack of a better word) even without a corresponding method. As far as syntax for calling a method just using it’s named symbol, there are two ways you can do this. The first is to use send: class Greeter def hello( name ) puts “Hello, #{name}!” end end greeter = Greeter.new greeter.send( :hello, “World” ) # prints “Hello, World!” An alternate technique is to grab an actual reference to the method itself. This is available using the ‘method’ method: greeter = Greeter.new meth = greeter.method( :hello ) meth.call( “World” ) # same output This latter approach allows you to perform the name lookup only once, even if you need to call the method several times. It’s also useful when metaprogramming; you can grab a reference to an existing method before redefining it, then call the original method from inside the redefined method. Nifty! Jacob F. ---
**Author:** ![chris.irish](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/4bbf92/32.png) [@chris.irish](https://www.ruby-forum.com/u/chris.irish)\ **Post date:** [December 2, 2005, 10:55pm UTC](https://www.ruby-forum.com/t/make-a-symbol-represent-a-method/49337/5 "2005-12-02T22:55:22Z")
Hi – On Sat, 3 Dec 2005, Jacob F. wrote: > without a corresponding method. > True… though it’s a bit like saying, “It’s possible to create a > string even if you don’t use it as a hash key” 🙂 I’d put it more > simply: a symbol is a built-in data type which can be, and is, used > for many purposes both internally and in user-space. From the user > side, I don’t think there’s any special relation between the symbol :x > and a method called x. The use of one, in itself, never has any > implications for the other. > As far as syntax for calling a method just using it’s named symbol, > there are two ways you can do this. The first is to use send: > […] > An alternate technique is to grab an actual reference to the method > itself. This is available using the ‘method’ method: Neither of these actually requires a Symbol object, though (as opposed to a String). David – David A. Black removed\_email\_address@domain.invalid “Ruby for Rails”, forthcoming from Manning Publications, April 2006! ---
**Author:** ![chris.irish](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/4bbf92/32.png) [@chris.irish](https://www.ruby-forum.com/u/chris.irish)\ **Post date:** [December 2, 2005, 10:06pm UTC](https://www.ruby-forum.com/t/make-a-symbol-represent-a-method/49337/6 "2005-12-02T22:06:04Z")
Jacob F. wrote: > Sure thing. The symbol is not a reference to the method at all. What > puts “Hello, #{name}!” > greeter = Greeter.new > Jacob F. Thank’s everyone 🙂 ---
**Author:** ![chris.irish](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/4bbf92/32.png) [@chris.irish](https://www.ruby-forum.com/u/chris.irish)\ **Post date:** [December 2, 2005, 8:24pm UTC](https://www.ruby-forum.com/t/make-a-symbol-represent-a-method/49337/7 "2005-12-02T20:24:08Z")
On 12/2/05, Chris I. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > I just read a FAQ page online about Ruby symbols and someone mentions this > > Also, the entirely realistic reasoning for using symbols: If you > are going to refer to a method name, use a symbol. Because by > defining the method, the symbol exists anyway. > > Can someone show me an example of this? Is this referring to the method > of a class? It simply comes down to this. When you define a method the method definition is saved away and connected to a lookup table for the object you defined the message on. The key into that lookup table? A symbol representing the method’s name. So if I define: def hello puts “Hello, world!” end The body is complied into a Method object, and that Method object is then attached to the current self (Kernel, is you’re not in anything else) with the symbol :hello as the key. After defining the above, try this: send(:hello) Anytime you make a method call, it’s essentially just an invocation of send with the method name and arguments as paramenters. (Well, it’s a little more complicated, but that’s why I said “essentially”.) Anyways, the point of the quote from the FAQ is that just be defining the method hello, the symbol :hello already exists, since it’s used to index the receiver’s method table. So, if you’re going to be passing the method name around (common with metaprogramming), you save by using the already existing :hello symbol, instead of creating a new “hello” String object. I hope that makes sense… Jacob F. ---
**Author:** ![chris.irish](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/4bbf92/32.png) [@chris.irish](https://www.ruby-forum.com/u/chris.irish)\ **Post date:** [December 2, 2005, 9:41pm UTC](https://www.ruby-forum.com/t/make-a-symbol-represent-a-method/49337/8 "2005-12-02T21:41:48Z")
Jacob F. wrote: > > of a class? > > end > > little more complicated, but that’s why I said “essentially”.) > > Jacob F. K… I get it One more thing, Can I use the symbol to call a method and pass arguments to it? Or is it just a reference to the methods name so that’s not possible?