From: Dan Doel <djd15@...>
Date: 2003-11-20T02:43:20+09:00
Subject: Re: x.f! RCR

Michael Neumann wrote:

>Your suggestion is that delete_if does not delete anything (it creates a new
>array), where delete_if! would. Principle of Least Surprise? Not for me!
>  
>

That depends on your background, I suppose.  If I'm not mistaken, ! and 
? probably come from Scheme,
where ! is usually used to denote that it causes a side effect on the 
arguments.  Since Scheme advocates
functional programming,

(delete_if predicate list)

would return a new list with the proper elements deleted, while

(delete_if! predicate list)

would delete the elements in place (probably returning the list as well).

If you're writing in a functional manner, it's not at all surprising to 
expect a delete... or remove... function to
not modify the initial list (in fact it's almost a requirement if you 
want to prove certain correctness
requirements for a program).  In that case, the fact that there is no 
#delete_if that doesn't modify the base
list would be an inconvenience.  Not that Ruby's lists are exactly 
suited for functional programming, but
food for thought.

Cheers.

- Dan