From: Robert Klemme <shortcutter@...>
Date: 2007-02-04T20:20:06+09:00
Subject: Re: Proc vs lambda vs proc

On 04.02.2007 04:55, Minkoo Seo wrote:
> I got a question on Proc.new and lambda { ... }. AFAIK, there's two
> differences between Proc.new(=proc) and lambda.

I think you have it slightly wrong: "proc" and "lambda" are aliases 
while "Proc.new" works different.

 > The first one is that
> Proc.new does not check the number of arguments passed to it while
> lambda does.

Correct:

irb(main):001:0> f1 = Proc.new {|a,b|a+b}
=> #<Proc:0x003bb2d0@(irb):1>
irb(main):002:0> f2 = proc {|a,b|a+b}
=> #<Proc:0x003b1690@(irb):2>
irb(main):003:0> f3 = lambda {|a,b|a+b}
=> #<Proc:0x003a4d3c@(irb):3>
irb(main):004:0> f1[1,2]
=> 3
irb(main):005:0> f1[1,2,3]
=> 3
irb(main):006:0> f2[1,2,3]
ArgumentError: wrong number of arguments (3 for 2)
         from (irb):2
         from (irb):6:in `[]'
         from (irb):6
         from :0
irb(main):007:0> f3[1,2,3]
ArgumentError: wrong number of arguments (3 for 2)
         from (irb):3
         from (irb):7:in `[]'
         from (irb):7
         from :0
irb(main):008:0> f2[1,2]
=> 3
irb(main):009:0> f3[1,2]
=> 3

 > The secondis that lambda returns as we expect, i.e., it
> returns value, while Proc.new does not.

I do not understand what you mean here.  All three return what you 
expect (apart from an exception in the case of wrong # of arguments.

> Though Proc.new lacks several advantages that lambda has,

Which advantages do you refer to?

 > I guess
> there might be some situation where Proc.new is more suitable than
> lambda. As an example, some code blocks that have to executed
> thousands times might run more faster than lambda because it does not
> have to check the # of arguments, thereby decreasing computational
> overhead.

I suggest to benchmark a concrete example if you are interested in 
timings.  My guess is that the parameter checking overhead is negligible.

> What is your opinion?

I usually use lambda because it most resembles the term "lambda 
expression".  But I guess this is just a matter of taste / personal 
preference.

Kind regards

	robert