Compatible Array#flatten

Array#flatten with depth argument is useful.

[[1], [2], [[3], 4]].flatten(1)
#=> [1, 2, [3], 4]

That's been available since ruby 1.8.7, but older ruby such as ruby 1.8.6 doesn't support it.

Here is the pure-ruby implementation of Array#flatten. Use it in case.

	#!/usr/bin/ruby
	#!/opt/local/bin/ruby for 1.8.7
	#!ruby191
	#!ruby192
	if RUBY_VERSION <= '1.8.6'
	class Array
	alias orig_flatten flatten
	def flatten(depth = -1)
	if depth < 0
	orig_flatten
	elsif depth == 0
	self
	else
	inject([]) {|m, i|
	Array === i ? m + i : m << i
	}.flatten(depth - 1)
	end
	end
	end
	end
	p RUBY_VERSION
	p [1, 2, 3].flatten == [1, 2, 3]
	p [1, 2, [3]].flatten == [1, 2, 3]
	p [[1], [2], [3, 4]].flatten == [1, 2, 3, 4]
	p [[1], [2], [[3], 4]].flatten == [1, 2, 3, 4]
	p [1, 2, 3].flatten(1) == [1, 2, 3]
	p [1, 2, [3]].flatten(1) == [1, 2, 3]
	p [[1], [2], [3, 4]].flatten(1) == [1, 2, 3, 4]
	p [[1], [2], [[3], 4]].flatten(1) == [1, 2, [3], 4]
	p [[1, 2], [[[3], 4]]].flatten(1) == [1, 2, [[3], 4]]
	p [[1], [2], [[3], 4]].flatten(2) == [1, 2, 3, 4]
	p [[1, 2], [[[3], 4]]].flatten(2) == [1, 2, [3], 4]
	p [[1, 2], [[[3], 4]]].flatten(3) == [1, 2, 3, 4]
	p [[1, 2], [[[3], 4]]].flatten(-1) == [1, 2, 3, 4]
	p [[1, 2], [[[3], 4]]].flatten(0) == [[1, 2], [[[3], 4]]]

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I used it for my library spawn-for-legacy to support ruby 1.8.6.

Rails programmers don't need this code. Rails now only supports ruby newer than 1.8.7.