Values

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:

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

ruby p = OpenStruct.new(x: 1) # => #<OpenStruct x=1> p.y # => nil

Struct and OpenStruct objects are mutable:

ruby p = Point.new(1, 2) p.x = 2 p.x # => 2

ruby 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:

ruby 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:

ruby 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:

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

Values can copy and replace fields using a hash:

ruby 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:

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

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

```ruby 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).