Module: Structure

Defined in:
lib/structure.rb,
lib/structure/rbs.rb,
lib/structure/types.rb,
lib/structure/builder.rb,
lib/structure/version.rb

Overview

A library for parsing data into immutable Ruby Data objects with type coercion

Defined Under Namespace

Modules: RBS, Types Classes: Builder

Constant Summary collapse

VERSION = 
"4.1.0"

Class Method Summary collapse

Class Method Details

.new {|Builder| ... } ⇒ Class

Creates a new Data class with attribute definitions and type coercion

Examples:

Basic usage

Person = Structure.new do
  attribute :name, String
  attribute :age, Integer
end

person = Person.parse(name: "Alice", age: "30")
person.name # => "Alice"
person.age  # => 30

Yields:

  • (Builder) —

    Block for defining attributes using the DSL

Returns:

  • (Class) —

    A Data class with a parse method



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# File 'lib/structure.rb', line 22

def new(&block)
  builder = Builder.new
  builder.instance_eval(&block) if block

  # @type var klass: untyped
  klass = Data.define(*builder.attributes)

  # Enable custom method definitions by evaluating block on the class
  if block
    # Provide temporary dummy DSL methods to prevent NoMethodError during class_eval
    klass.define_singleton_method(:attribute) { |*args, **kwargs, &blk| }
    klass.define_singleton_method(:attribute?) { |*args, **kwargs, &blk| }
    klass.define_singleton_method(:after_parse) { |&blk| }

    # Evaluate block in class context for method definitions
    klass.class_eval(&block)

    # Remove temporary DSL methods
    klass.singleton_class.send(:remove_method, :attribute)
    klass.singleton_class.send(:remove_method, :attribute?)
    klass.singleton_class.send(:remove_method, :after_parse)
  end

  # Override initialize to make optional attributes truly optional
  optional_attrs = builder.optional
  unless optional_attrs.empty?
    klass.class_eval do
      alias_method(:__data_initialize__, :initialize)

      define_method(:initialize) do |**kwargs| # steep:ignore
        optional_attrs.each do |attr|
          kwargs[attr] = nil unless kwargs.key?(attr)
        end
        __data_initialize__(**kwargs) # steep:ignore
      end
    end
  end

  builder.predicate_methods.each do |pred, attr|
    klass.define_method(pred) { !!public_send(attr) }
  end

  # Store metadata on class to avoid closure capture (memory optimization)
  meta = {
    types: builder.types,
    defaults: builder.defaults,
    mappings: builder.mappings,
    coercions: builder.coercions(klass),
    after_parse: builder.after_parse_callback,
    required: builder.required,
  }.freeze
  klass.instance_variable_set(:@__structure_meta__, meta)
  klass.singleton_class.attr_reader(:__structure_meta__)

  # recursive to_h
  klass.define_method(:to_h) do
    klass.members.to_h do |m|
      v = public_send(m)
      value = case v
      when Array then v.map { |x| x.respond_to?(:to_h) && x ? x.to_h : x }
      when ->(x) { x.respond_to?(:to_h) && x } then v.to_h
      else v
      end
      [m, value]
    end
  end

  # parse accepts JSON-ish hashes + optional overrides hash
  # overrides is a positional arg (not **kwargs) to avoid hash allocation when unused
  #
  # @type self: singleton(Data) & _StructuredDataClass
  # @type var final: Hash[Symbol, untyped]
  klass.singleton_class.define_method(:parse) do |data = {}, overrides = nil|
    return data if data.is_a?(self)

    unless data.respond_to?(:merge!)
      raise TypeError, "can't convert #{data.class} into #{self}"
    end

    overrides&.each { |k, v| data[k.to_s] = v }

    final       = {}
    mappings    = __structure_meta__[:mappings]
    defaults    = __structure_meta__[:defaults]
    after_parse = __structure_meta__[:after_parse]
    required    = __structure_meta__[:required]

    # Check for missing required attributes
    required.each do |attr|
      from = mappings[attr]
      next if data.key?(from) || data.key?(from.to_sym) || defaults.key?(attr)

      raise ArgumentError, "missing keyword: :#{attr}"
    end

    mappings.each do |attr, from|
      value = data.fetch(from) do
        data.fetch(from.to_sym) do
          defaults[attr]
        end
      end

      if value
        coercion = __structure_meta__[:coercions][attr]
        value = coercion.call(value) if coercion
      end

      final[attr] = value
    end

    obj = new(**final)
    after_parse&.call(obj)
    obj
  end

  klass
end