Ruby - lambda vs. Proc.new

Question

Possible Duplicate:
What's the difference between a proc and a lambda in Ruby?

When run this Ruby code:

def func_one
    proc_new = Proc.new {return "123"}
    proc_new.call
    return "456"
end

def func_two
    lambda_new = lambda {return "123"}
    lambda_new.call
    return "456"
end

puts "The result of running func_one is " + func_one
puts ""
puts "The result of running func_two is " + func_two

The result that I get is as follows:

The result of running func_one is 123

The result of running func_two is 456

As for func_two, where is the the value of the first return, that is, 123?

Thanks.

Answer 1

This is one of the main differences between Procs and lambdas.

A return in a Proc returns from its enclosing block/method, while a return in a lambda simply returns from the lambda. When you call the lambda inside the func_two, it simply returns its value in place, which is not saved.

Read on Procs v. lambdas here: http://en.wikibooks.org/wiki/Ruby_Programming/Syntax/Method_Calls

See duplicate SO question: Why does explicit return make a difference in a Proc?

EDIT:

To further illustrate this difference, swap func_one and func_two for blocks and see what happens:

> begin; lambda { return 1 }.call end
1
> begin; Proc.new { return 1 }.call end
LocalJumpError: unexpected return
...