Allow to inherit one page from another

To allow reuse of common sections and to allow to add
or remove sections for specific cases.

Author: Envek

README.md

@@ -21,7 +21,7 @@ Or install it yourself as:
 ## Usage
 
 ```ruby
-class class IndexPage < Tram::Page
+class IndexPage < Tram::Page
   # See dry-initializer
   param  :account
   option :readonly, optional: true
@@ -52,6 +52,21 @@ IndexPage.new(Account.find(99)).to_h(except: :collection)
 IndexPage.new(Account.find(99)).to_h(only: :collection)
 ```
 
+Inheritance of page objects is supported:
+
+```ruby
+class FancyIndexPage < IndexPage
+  section :collection, skip: true
+  section :fancy_collection
+
+  def fancy_collection
+    collection.map(&:fancy)
+  end
+end
+
+FancyIndexPage.new(Account.find(99)).to_h
+```
+
 ## Development
 
 After checking out the repo, run `bin/setup` to install dependencies. Then, run `rake spec` to run the tests. You can also run `bin/console` for an interactive prompt that will allow you to experiment.

lib/tram/page.rb

@@ -7,15 +7,14 @@ class << self
     attr_accessor :i18n_scope
 
     def section(name, options = {})
-      @__sections ||= []
+      @__sections ||= {}
 
       n = name.to_sym
-      if @__sections.map(&:first).include?(n)
-        raise "Section #{n} already exists"
-      end
+      return @__sections.delete(n) if options[:skip]
+      raise "Section #{n} already exists" if @__sections.key?(n)
 
       n = define_section_method(n, options)
-      @__sections << [n, options]
+      @__sections[n] = options
     end
 
     def url_helper(name)
@@ -30,6 +29,10 @@ def define_section_method(n, options)
       define_method(n) { instance_exec(&options[:value]) }
       n
     end
+
+    def inherited(subclass)
+      subclass.instance_variable_set(:@__sections, @__sections.dup)
+    end
   end
 
   def to_h(options = {})
@@ -51,7 +54,7 @@ def page_methods(options)
     methods = self.class.instance_variable_get(:"@__sections") || []
     except = Array(options[:except])
     only = Array(options[:only])
-    methods.reject do |(name, opts)|
+    methods.reject do |name, opts|
       (except.any? && except.include?(name)) ||
         (only.any? && !only.include?(name)) ||
         __hide?(opts)

spec/spec_helper.rb

@@ -5,6 +5,7 @@
 require "tram/page"
 require "support/blank_page"
 require "support/example_page"
+require "support/inherited_page"
 
 RSpec.configure do |config|
   # Enable flags like --only-failures and --next-failure

spec/support/inherited_page.rb

@@ -0,0 +1,10 @@
+# frozen_string_literal: true
+
+class InheritedPage < ExamplePage
+  section :baz, skip: true
+  section :bam
+
+  def bam
+    baz.upcase
+  end
+end

spec/tram/inherited_page_spec.rb

@@ -0,0 +1,16 @@
+# frozen_string_literal: true
+
+require "spec_helper"
+
+RSpec.describe InheritedPage do
+  subject { described_class.new("test") }
+
+  it "returns data hash with new and without skipped fields" do
+    expect(subject.to_h).to eq(bar: "test", foo: "test", bam: "TEST")
+  end
+
+  it "doesn't change behaviour of the parent class" do
+    expect(described_class.superclass.new("test").to_h).to \
+      eq(bar: "test", foo: "test", baz: "test")
+  end
+end