use parent when possible (#54)

If possible, child classes can use the parent's equivalent member and
pointer constructor.

ChangeLog.md

@@ -9,10 +9,15 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
  - Python class generation.
  - Perl class generation.
 
-## [0.4.0] - 2020-01-02
+## [0.4.0] - 2020-01-08
 ### Added
  - Inequality conditions for rules (less-than, less-than-equal, greater-than,
    greater-than-equal).
+ - Classes who's parent wraps the same equivalent struct will re-use the
+   equivalent pointer member of the parent class.
+ - Pointer classes who's parent wraps the same equivalent struct will use the
+   parent's pointer constructor as the initializer for their own pointer
+   constructor.
 
 ## [0.3.0] - 2020-01-01
 ### Added

lib/wrapture/class_spec.rb

@@ -172,7 +172,12 @@ def overloads?(parent_spec)
 
     # The name of the parent of this class, or nil if there is no parent.
     def parent_name
-      @spec['parent']['name'] if @spec.key?('parent')
+      @spec['parent']['name'] if child?
+    end
+
+    # Determines if this class is a wrapper for a struct pointer or not.
+    def pointer_wrapper?
+      @spec['type'] == 'pointer'
     end
 
     # The name of the equivalent struct of this class.
@@ -208,6 +213,11 @@ def type?(type)
 
     private
 
+    # True if the class has a parent.
+    def child?
+      @spec.key?('parent')
+    end
+
     # Gives the content of the class declaration to a block, line by line.
     def declaration_contents
       yield "#ifndef #{header_guard}"
@@ -222,7 +232,7 @@ def declaration_contents
       yield "namespace #{@spec['namespace']} {"
       yield
 
-      parent = if @spec.key?('parent')
+      parent = if child?
                  ": public #{parent_name} "
                else
                  ''
@@ -237,7 +247,7 @@ def declaration_contents
       end
 
       yield
-      yield "    #{@struct.declaration equivalent_name};"
+      equivalent_member_declaration { |line| yield "    #{line}" }
       yield
 
       member_constructor_declaration { |line| yield "    #{line}" }
@@ -273,7 +283,7 @@ def declaration_includes
         includes.concat(const.declaration_includes)
       end
 
-      includes.concat(@spec['parent']['includes']) if @spec.key?('parent')
+      includes.concat(@spec['parent']['includes']) if child?
 
       includes.uniq
     end
@@ -341,6 +351,22 @@ def definition_includes
       includes.uniq
     end
 
+    # Yields the declaration of the equivalent member if this class has one.
+    #
+    # A class might not have an equivalent member if it is able to use the
+    # parent class's, for example if the child class wraps the same struct.
+    def equivalent_member_declaration
+      if child?
+        parent_spec = @scope.type(parent_name)
+        member_reusable = !parent_spec.nil? &&
+                          parent_spec.struct_name == @struct.name &&
+                          parent_spec.pointer_wrapper? == pointer_wrapper?
+        return if member_reusable
+      end
+
+      yield "#{@struct.declaration(equivalent_name)};"
+    end
+
     # Gives the name of the equivalent struct.
     def equivalent_name
       "#{'*' if pointer_wrapper?}equivalent"
@@ -467,7 +493,8 @@ def pointer_constructor_definition
         func.constructor? && func.signature.start_with?(signature_prefix)
       end
 
-      yield "#{@spec['name']}::#{pointer_constructor_signature} {"
+      initializer = pointer_constructor_initializer
+      yield "#{@spec['name']}::#{pointer_constructor_signature} #{initializer}{"
 
       if pointer_wrapper?
         yield '  this->equivalent = equivalent;'
@@ -481,16 +508,25 @@ def pointer_constructor_definition
       yield '}'
     end
 
+    # The initializer for the pointer constructor, if one is available, or an
+    # empty string if not.
+    def pointer_constructor_initializer
+      if pointer_wrapper? && child?
+        parent_spec = @scope.type(parent_name)
+        parent_usable = !parent_spec.nil? &&
+                        parent_spec.pointer_wrapper? &&
+                        parent_spec.struct_name == @struct.name
+        return ": #{parent_name}( equivalent ) " if parent_usable
+      end
+
+      ''
+    end
+
     # The signature of the constructor given an equivalent strucct pointer.
     def pointer_constructor_signature
       "#{@spec['name']}( #{@struct.pointer_declaration 'equivalent'} )"
     end
 
-    # Determines if this class is a wrapper for a struct pointer or not.
-    def pointer_wrapper?
-      @spec['type'] == 'pointer'
-    end
-
     # The signature of the constructor given an equivalent struct type.
     def struct_constructor_signature
       "#{@spec['name']}( #{@struct.declaration 'equivalent'} )"

test/fixtures/pointer_class_and_child.yml

@@ -0,0 +1,15 @@
+version: "0.4.0"
+classes:
+  - name: "ParentPointer"
+    namespace: "wrapture_test"
+    type: "pointer"
+    equivalent-struct:
+      name: "wrapped_struct"
+  - name: "ChildPointer"
+    namespace: "wrapture_test"
+    type: "pointer"
+    parent:
+      name: "ParentPointer"
+      includes: "ParentPointer.hpp"
+    equivalent-struct:
+      name: "wrapped_struct"

test/test_pointer_class.rb

@@ -2,7 +2,7 @@
 
 # frozen_string_literal: true
 
-# Copyright 2019 Joel E. Anderson
+# Copyright 2019-2020 Joel E. Anderson
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
 # you may not use this file except in compliance with the License.
@@ -68,4 +68,21 @@ def test_pointer_class
 
     File.delete(*classes)
   end
+
+  def test_pointer_class_and_child
+    test_spec = load_fixture('pointer_class_and_child')
+
+    spec = Wrapture::Scope.new(test_spec)
+
+    classes = spec.generate_wrappers
+    validate_wrapper_results(test_spec, classes)
+
+    equivalent_signature = 'struct wrapped_struct \*equivalent;'
+    refute(file_contains_match('ChildPointer.hpp', equivalent_signature))
+
+    parent_initializer = 'equivalent \) : ParentPointer\('
+    assert(file_contains_match('ChildPointer.cpp', parent_initializer))
+
+    File.delete(*classes)
+  end
 end