Difference between lambda and def method_name in Ruby

Question

I am reading along in pickaxe 1.9 and the author uses lambda like this:

bo = lambda {|param| puts "You called me with #{param}"}
bo.call 99     => 'You called me with 99'
bo.call "cat"  => 'You called me with cat'

My question is this: How is this any better/worse/different than just defining a method that does that same thing? Like so:

def bo(param)
  puts "You called me with #{param}"
end

bo("hello") => 'You called me with hello'

To me the lambda syntax seems much more confusing and spaghetti-like.

Answer 1

Lambdas:

• are variations of Procs,
• can be converted to/from blocks,
• do not begin a new closure scope (meaning you can access variables defined outside the scope of your lambda, unlike def),
• can be passed around as variables.

I recommend checking out this article that explain procs, blocks, and lambdas.

Edit: This link is outdated. For future reference, try this article

Answer 2

The advantage that defining a lambda gives you is that you can then pass that lambda object as an attribute to another method.

def method1 &b
  #... some code
  b.call
end

def method2 &b
  #... some more code...
  b.call
end

def method3 &b
  b.call
  #even more code here
end

myCallback = lambda { "this is a callback that can be called from several methods"}

You can then use it like this:

method1 &myCallback
method2 &myCallback
method3 &myCallback

And the beauty of this, is that you only wrote of code of the callback once, but used it 3 times....

I would recommend you take a look at this link for further reading :)