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TypeStruct

Imitating static typed struct.

All type is checked by === method.

Motivation

I don't like Hash

p h #=> {color: 'red', width: 120, height: 200}

No name

What is this a data? We cannot know this name.

Where is this an instance from? How do we grep doing?

Bad syntax

h[:widht] #=> Cannot detect typo
#=> nil
h.dig(:widht) #=> ditto
#=> nil
h.fetch(:widht) #=> Can detect typo, But too long and cannot know suggestion from did_you_mean gem
# KeyError: key not found: :widht

Too freedom

# Where is from `who` key? Is this expected?
p h #=> {color: 'red', width: 120, height: 200, who: 'are you?'}

I like Struct

Grepable Name

Circle = Struct.new(:color, :width, :height)
circle = Circle.new('red', 120, 200)

Good syntax

circle.color
#=> 'red'
circle.widht
# NoMethodError:
Did you mean?  width
               width=

Strictly members

circle.who = "are you?"
# NoMethodError: undefined method `who='

Evolution

  • Can use keyword arguments
  • Add Type system
  • Recursive Mapping

This is the TypeStruct.

Usage

Check type

Sample = TypeStruct.new(
  str: String,
  reg: /exp/,
  num: Integer,
  any: Object,
)

sample = Sample.new(
  str: "instance of String",
  reg: "match to regexp",
  num: 10,
  any: true,
)

p sample
#=> #<Sample str="instance of String", reg="not match to regexp", num=10, any=true>

p sample.to_h
#=> {:str=>"instance of String", :reg=>"not match to regexp", :num=>10, :any=>true}

p sample.str
#=> "instance of String"

sample.string #=> NoMethodError
sample.str = 1 #=> TypeError

Recursive Mapping

Generate object from hash by recursive.

Like JSON package of golang and crystal-lang.

Point = TypeStruct.new(
  x: Integer,
  y: Integer,
)
Color = TypeStruct.new(
  code: /\A#[0-9a-f]{6}\z/i,
)
Line = TypeStruct.new(
  start: Point,
  end: Point,
  color: Color,
)

hash = JSON.parse(%({"start":{"x":3,"y":10},"end":{"x":5,"y":9},"color":{"code":"#CAFE00"}}))
line = Line.from_hash(hash)

p line
#=> #<Line start=#<Point x=3, y=10>, end=#<Point x=5, y=9>, color=#<Color code="#CAFE00">>
p line.start.y
#=> 10
line.stort
#=> NoMethodError

Four special classes

Union

Union is an object express class that some classes as one class like crystal Union.

Union#=== check all object with === method.

Foo = TypeStruct.new(
  bar: TypeStruct::Union.new(TrueClass, FalseClass)
)
p Foo.new(bar: false) #=> #<Foo bar=false>

or add Class#| method by refinements

require "type_struct/ext"
using TypeStruct::Union::Ext
Foo = TypeStruct.new(
  bar: TrueClass | FalseClass,
)

ArrayOf

ArrayOf is an object express array type.

ArrayOf#=== check all item with === method.

Bar = TypeStruct.new(
  baz: TypeStruct::ArrayOf.new(Integer),
)
p Bar.new(baz: [1, 2, 3]) #=> #<Bar baz=[1, 2, 3]>

HashOf

HashOf#=== check all keys and values with === method.

Baz = TypeStruct.new(
  qux: TypeStruct::HashOf.new(String, TypeStruct::ArrayOf.new(Integer))
)
p Baz.new(qux: { "a" => [1, 2, 3] }) #=> #<Baz qux={"a"=>[1, 2, 3]}>
p Baz.from_hash(qux: { "a" => [1, 2, 3] }) #<Baz qux={"a"=>[1, 2, 3]}>
p Baz.new(qux: { :a  => [1, 2, 3] }) #=> TypeError
p Baz.new(qux: { "a" => [1, 2, nil] }) #=> TypeError

Interface

Interface is an object for duck typing like golang interface.

Interface#=== check all method using respond_to?

Foo = TypeStruct.new(
  bar: TypeStruct::Interface.new(:read, :write)
  # or Interface.new(:read, :write) on required 'type_struct/ext'
)
Foo.new(bar: $stdin)
Foo.new(bar: 1) #=> TypeError

Mix

require "type_struct/ext"
using TypeStruct::Union::Ext
Baz = TypeStruct.new(
  qux: ArrayOf(Integer | TrueClass | FalseClass) | NilClass
)
p Baz.new(qux: [1]) #=> #<AAA::Baz qux=[1]>
p Baz.new(qux: [true, false]) #=> #<AAA::Baz qux=[true, false]>
p Baz.new(qux: nil) #=> #<AAA::Baz qux=nil>
p Baz.new(qux: 1) #=> TypeError
p Baz.from_hash(qux: [1, 2, false, true]) #=> #<A::Baz qux=[1, 2, false, true]>

Auto Generator

$ echo '{"posts": [{"number":10491,"name":"ksss"}]}' | ruby -r type_struct/generator/json
Post = TypeStruct.new(
  number: Integer,
  name: String,
)
AutoGeneratedStruct = TypeStruct.new(
  posts: ArrayOf(Post),
)

Installation

Add this line to your application's Gemfile:

gem 'type_struct'

And then execute:

$ bundle

Or install it yourself as:

$ gem install type_struct

License

The gem is available as open source under the terms of the MIT License.