Ruby

* Document-class: Numeric

*

* Numeric is the class from which all higher-level numeric classes should inherit.

*

* Numeric allows instantiation of heap-allocated objects. Other core numeric classes such as

* Integer are implemented as immediates, which means that each Integer is a single immutable

* object which is always passed by value.

*

* a = 1

* puts 1.object_id == a.object_id #=> true

*

* There can only ever be one instance of the integer +1+, for example. Ruby ensures this

* by preventing instantiation and duplication.

*

* Integer.new(1) #=> NoMethodError: undefined method `new' for Integer:Class

* 1.dup #=> TypeError: can't dup Fixnum

*

* For this reason, Numeric should be used when defining other numeric classes.

*

* Classes which inherit from Numeric must implement +coerce+, which returns a two-member

* Array containing an object that has been coerced into an instance of the new class

* and +self+ (see #coerce).

*

* Inheriting classes should also implement arithmetic operator methods (<code>+</code>,

* <code>-</code>, <code>*</code> and <code>/</code>) and the <code><=></code> operator (see

* Comparable). These methods may rely on +coerce+ to ensure interoperability with

* instances of other numeric classes.

*

* class Tally < Numeric

* def initialize(string)

* @string = string

* end

*

* def to_s

* @string

* end

*

* def to_i

* @string.size

* end

*

* def coerce(other)

* [self.class.new('|' * other.to_i), self]

* end

*

* def <=>(other)

* to_i <=> other.to_i

* end

*

* def +(other)

* self.class.new('|' * (to_i + other.to_i))

* end

*

* def -(other)

* self.class.new('|' * (to_i - other.to_i))

* end

*

* def *(other)

* self.class.new('|' * (to_i * other.to_i))

* end

*

* def /(other)

* self.class.new('|' * (to_i / other.to_i))

* end

* end

*

* tally = Tally.new('||')

* puts tally * 2 #=> "||||"

* puts tally > 1 #=> true