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:

“by Point = Struct.new(:x, :y) Point.new(1)

=> #

Maruku could not parse this XML/HTML: 
<struct Point x=1, y=nil>

“

“by p = OpenStruct.new(x: 1)

=> #

Maruku could not parse this XML/HTML: 
<OpenStruct x=1>

p.y

=> nil

“

Struct and OpenStruct objects are mutable:

“by p = Point.new(1, 2) p.x = 2 p.x

=> 2

“

“by 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:

“by 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:

“by 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

Maruku could not parse this XML/HTML: 
<main>

“

Features

Values also provides an alternative constructor which takes a hash:

“by p = Point.with(x: 3, y: 4) p.x

=> 3

“

Values can copy and replace fields using a hash:

“by p = Point.with(x: 1, y: -1) q = p.with(y: 2)

=> #

Maruku could not parse this XML/HTML: 
<Point x=1, y=2>

“

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

“by Point.with(x: 1, y: -1).to_h

=>

“

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

“by class Point < Value.new(:x, :y) def to_s “

Maruku could not parse this XML/HTML: 
<Point at (#{x}, #{y})>"
  end
end

p = Point.new(1, 2) p.to_s

=> “

Maruku could not parse this XML/HTML: 
<Point at (1, 2)>"

“

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