From: Kyle Schmitt <kyleaschmitt@...>
Date: 2008-09-25T05:45:13+09:00
Subject: Getting the right class with inheritance and super()

I'm wondering what the _right_ way is to go about getting the right
class with inheritance and super()

Take the following class I'm using for a graphing tool: Like the name
says, it creates a fixed size array.  The << operator allows you to
use it as if it were a circular queue of sorts, and the size= method
allows you to re-size the array if necessary.

The issue is that while << works fine, the results from + and - return
an Array, not a FixedSizeArray, UNLESS I run the returned value
through a FixedSizeArray.new(), and somehow, that just seems wrong and
wasteful.

Am I crazy?  Is that really the right way?

class FixedSizeArray<Array
	def initialize(size=1,fill=nil)
		#Sizes under one don't make sense
		if size.is_a?Array
			super(size)
		else
			super(size,fill)
		end
		self
	end

	def size=(newsize)
		unless length==newsize
			if length > newsize
				self.slice!(Range.new(0,length-newsize-1))
			elsif length < newsize
				self.unshift(*Array.new(newsize-length){0})
			end
		end
		size
	end
	
	def <<(data)
		self.shift()
		super(data)
		self
	end

	def -(data)
		#Works, but feels somehow...wasteful and wrong
		FixedSizeArray.new(super(data).unshift(*Array.new(size-super(data).length,nil)))
	end

	def +(data)
		#Works, but feels somehow...wasteful and wrong
		FixedSizeArray.new(super(data).slice(Range.new(data.length,size+data.length)))
	end
	
end