From: Dave Thomas <Dave@...>
Date: 2002-12-02T01:58:29+09:00
Subject: Re: [FAQ] What do some of Ruby's symbols mean?

Austin Ziegler <austin@halostatue.ca> writes:

> <=>, <=, <, >=, >, ==, !=
>     1.  Relational operators, used to determine the relative
>         equality of values. All of these symbols, excepting "!=",
>         are defined as methods on classes. The most common way of
>         implementing these values is through the [Comparable] mixin,
>         where it is only necessary to define "<=>" (which must
>         return a value of -1, 0, or +1).

Actually, it's looser than that: the spaceship can return less than
zero, zero, or greater than zero.

> +, -, *, /, %, **
>     1.  Binomial arithmetic operators representing addition (3 + 2),

Simple typo for 'binary'.


>     2.  "<<" also opens an object for modification to make a
>         singleton-object (one which is not quite like any other
>         object of its class). In the example below, only the Car
>         object referred to by "camaro" will have the method
>         "has_flames?".

Possibly "Creates a new class based on a particular object. These
object-specific classes are called 'singletons' (or singleton
classes). In the example..."

> 
>           camaro = Car.new
>           class << camaro
>             def has_flames?
>               true
>             end
>           end

If a singleton class for a object already exists, << simply modifies
it, rather than creating a new one.

A common idiom is "class <<self;methods...;end", found inside class
definitions. As 'self' inside a class definition references the class
object, this somewhat strange construct ends up adding methods at the
class (as opposed to instance) level.