From: "Hal E. Fulton" <hal9000@...>
Date: 2001-05-16T13:23:16+09:00
Subject: [ruby-talk:15234] Pluggable sorting - How would you do it?

Hello all,

I was thinking about this today. I'd like to be able to define 
some "ways of sorting" objects (i.e., by different fields)
and just plug them in.

Passing a block to "sort" is neat, but it's a little more 
intrusive than I have in mind.

I thought about a Proc object or something... but I ended
up doing it this way (see code below).

It works. But I'm sure many of you have better ideas.

How would *you* do it?

Hal


#########################
class Foo
  attr_reader :str, :int, :chr

  def initialize(str, int, chr)
    @str, @int, @chr = str, int, chr
  end

  def inspect
    "#@str #@int #@chr"
  end
end

class Array
  def sortBy(sym)
    expr = sym.id2name + "(x,y)"
    self.sort { |x,y| instance_eval(expr) }
  end
end

def Str(x,y)
  x.str <=> y.str
end

def Int(x,y)
  x.int <=> y.int
end

def Chr(x,y)
  x.chr <=> y.chr
end


x = [ Foo.new("abc", 237, ?a), Foo.new("xyz", 365, ?u),
      Foo.new("dfg", 666, ?j), Foo.new("lkg", 111, ?i),
      Foo.new("fkt", 999, ?s), Foo.new("krd", 123, ?t),
      Foo.new("rej", 451, ?y), Foo.new("yhd", 555, ?k),
      Foo.new("ajs", 143, ?l), Foo.new("jud", 199, ?f)]

a = x.sortBy :Str
b = x.sortBy :Int
c = x.sortBy :Chr

a.each { |x| p x }
puts "------"
b.each { |x| p x }
puts "------"
c.each { |x| p x }