Why should I use lambda/proc ?Explain it's importance [duplicate]

Question

I am new to ruby, and while learning it I didn't understand the concept of lambdas or procs. I know lambda and proc are the blocks of code that have been bound to a set of local variables. But I don't understand their use.

So

what advantage does a programmer get from it?

I had asked this question in past and got marked as duplicate and was given a link that had totally unrelated answered so please before marking it as duplicate or scolding me please view the answers of other links by yourself first.

Answer 1

This is a broad question. You're basically asking "why are closures important?". Two uses that come to mind for me are:

DISCLAIMER: I haven't actually run any of this code, but it should get the point across.

1. Delayed execution of code. If I want to pass some code as a callback (e.g. Rails' after_create), I can use a closure to "hook" into Rails by passing a block. That block has the context of the current class, but it doesn't need to get run until Rails says so.

   class SuperClass
     def self.after_create(&block)
       @__after_create = block
     end
   
     def self.create
       # do normal create logic
       instance = self.new
       if @__after_create
         @__after_create.call(instance)
       end
     end
   end
   
   class MyClass < SuperClass
     after_create {|instance| instance.log}
   
     def log
       puts 'hello world!'
     end
   end
   
   MyClass.create
   

2. Passing functions as parameters. This makes it easier to do things like write a generic tree traversal algorithm that just passes each node of the tree to some function:

   def Tree.elements
     ["hello", "world!"]
   end
   
   def Tree.traverse(&block)
     elements.each {|el| block.call(el)}
   end
   
   Tree.traverse {|el| puts el} # "hello" "world!"
   Tree.traverse {|el| puts el.size} # "5" "6"