Skip to content

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

License

Notifications You must be signed in to change notification settings

tcrayford/Values

Repository files navigation

Values

Gem Version Gem Downloads CI Build Status Code Coverage Yard Docs

Summary

Values is a tiny library for creating value objects in ruby.

Classes created using Value mostly look like classes created using Struct or OpenStruct, but fix two problems with those:

Problems with Struct and OpenStruct

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

Point = Struct.new(:x, :y)
Point.new(1)
# => #<struct Point x=1, y=nil>
p = OpenStruct.new(x: 1)
# => #<OpenStruct x=1>
p.y
# => nil

Struct and OpenStruct objects are mutable:

p = Point.new(1, 2)
p.x = 2
p.x
# => 2
p = OpenStruct.new(x: 1, y: 2)
p.x = 2
p.x
# => 2

Values is Better

Values fixes both of the above problems.

Constructors require expected arguments:

Point = Value.new(:x, :y)
Point.new(1)
# => 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>

Instances are immutable:

p = Point.new(1, 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>

Features

Values also provides an alternative constructor which takes a hash:

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

Value classes can be converted to a hash, like OpenStruct:

Point.with(x: 1, y: -1).to_h
# => {:x=>1, :y=>-1}

Values also supports customization of value classes inheriting from Value.new:

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

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

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

About

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

Resources

License

Stars

Watchers

Forks

Packages

No packages published

Languages