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Simple immutable value objects for ruby (the readme is longer than the code)
branch: master

Merge pull request #24 from ms-ati/add-copy-method

Add #with method supporting hash args
latest commit 998f7df719
@tcrayford authored

Values is a tiny library for creating value objects in ruby. These mostly look like classes created using Struct, but fix two problems with those:

Struct constructors can take less than the default number of arguments and set other fields as nil:

Point =, :y)
# => #<struct Point x=1, y=nil>

Structs are also mutable:

Point =, :y)
p =, 2)
p.x = 2
# => 2

Values fixes both of these:

Point =, :y)
# => ArgumentError: wrong number of arguments, 1 for 2
# from /Users/tcrayford/Projects/ruby/values/lib/values.rb:7:in `block (2 levels) in new
# from (irb):5:in new
# from (irb):5
# from /usr/local/bin/irb:12:in `<main>

p =, 2)
p.x = 1
# => NoMethodError: undefined method x= for #<Point:0x00000100943788 @x=0, @y=1>
# from (irb):6
# from /usr/local/bin/irb:12:in <main>

Values also provides an alternative constructor which takes a hash:

p = Point.with(x: 3, y: 4)
# => 3

Values can copy and replace fields using a hash:

p = Point.with(x: 1, y: -1)
q = p.with(y: 2)
# => #<Point x=1, y=2>

Values also supports customization of value classes inheriting from

class Point <, :y)
  def to_s
    "<Point at (#{x}, #{y})>"

p =, 2)
# => "<Point at (1, 2)>"

Values does NOT have all the features of Struct (nor is it meant to).

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