From: Eric MSP Veith <eveith@...>
Date: 2010-09-14T23:43:51+09:00
Subject: Re: method! and method?

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On Tuesday 14 September 2010, Gene Angelo <web.gma@gmail.com> wrote:
> I am trying to find the meaning of ! and ? appended to method names but
> I cannot find what they mean. Can someone explain?

First of all, it's a convention, nothing hard-wired.

The question mark is probably the easier to explain: It marks a boolean-
returning getter method. Where in e.g. Java you'd write isFile(..) or 
getStuff(..), with Ruby, it's just file? or stuff?.

The exclamation mark is harder to grasp. It's meaning is along the lines of 
"pay attention with this method." Most commonly it is used to demark a 
destructive twin of another method. E.g., there can be a #sort and a #sort! 
method. While the first one would return a sorted copy of the original, the 
second would modify the original itself. There is, however, no sense in 
marking every destructive method with an exclamation mark. A File#delete 
method is obvious enough, there's no need for a File#delete!. Think of it as 
the evil twin of the one without the exclamation mark. :-)

HTH.

			Eric
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