From: Max Muermann <ruby@...>
Date: 2006-10-09T08:09:56+09:00
Subject: Re: || explanation in ruby... in pseudolanguage

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On 10/9/06, Tuka Opaleye <tuka@yorn.net> wrote:
>
> Hi,
>
> I am trying to get my head around the || symbol used extensively in
> ruby. To me it is somewhat foreign still and I am trying a few exercise
> to make it click. Can anyone suggest a phrase (pseudolanguage) that
> accurately expresses the possible expressions using || ?


Well, || is just the standard boolean OR operator. What makes it a lot more
useful in Ruby than in other languages, is that only false and nil are
considered to be false, and a boolean or operation always returns the first
true (that is, not false or nil) value.

That's why

nil || 1

is not only true, but returns 1.

and

2 || 1

returns 2.

This is similar behaviour to the COALESCE function used in SQL: COALESCE(
a,b) will return b if a is null, and a otherwise.

So, in pseudo-language,

first_var || second_var || third_var

returns the first non-nil value.

There's also ||=, which is a very nice idiom for setting default values:

my_param ||= "some default value"

will assign "some default value" to my_param only if my_param is nil.

Hope that helps,

Cheers,
Max

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