libphobos/libdruntime/core/factory.d

   1 /* Create classes from their modules and names.
   2  *
   3  * Copyright: Copyright (C) D Language Foundation 2023
   4  * License:   $(LINK2 http://www.boost.org/LICENSE_1_0.txt, Boost License 1.0)
   5  * Authors:   Walter Bright, Steven Schveighoffer
   6  * Source:    $(DRUNTIMESRC core/_factory.d)
   7  */
   8
   9 module core.factory;
  10
  11 /**
  12  * Create instance of class specified by the module symbol and a string
  13  * representing the name of the class.
  14  * The class must either have no constructors or have
  15  * a default constructor.
  16  * Params:
  17  *   mod = symbol representing the module that the class is in
  18  *   classname = string representing the name of the class
  19  * Returns:
  20  *   null if failed
  21  * Example:
  22  * ---
  23  * module foo.bar;
  24  *
  25  * class C
  26  * {
  27  *     this() { x = 10; }
  28  *     int x;
  29  * }
  30  *
  31  * void main()
  32  * {
  33  *     auto c = cast(C)factory!(foo.bar)("C");
  34  *     assert(c !is null && c.x == 10);
  35  * }
  36  * ---
  37  */
  38 Object factory(alias mod)(string classname)
  39 {
  40     foreach(cl; _getModuleClasses!mod)
  41     {
  42         if (cl.stringof == classname)
  43             return cl.classinfo.create();
  44     }
  45     return null;
  46 }
  47
  48 @system unittest
  49 {
  50     Object valid_obj = factory!object("Object");
  51     Object invalid_obj = factory!object("__this_class_doesnt_exist__");
  52
  53     assert(valid_obj !is null);
  54     assert(invalid_obj is null);
  55 }
  56
  57 /**************************************
  58  * Retrieve as a tuple all the types of the top level classes in the module mod.
  59  */
  60 private template _getModuleClasses(alias mod) {
  61    alias result = _AliasSeq!();
  62    static foreach(m; __traits(allMembers, mod))
  63       static if(is(__traits(getMember, mod, m) == class))
  64          result = _AliasSeq!(result, __traits(getMember, mod, m));
  65    alias _getModuleClasses = result;
  66 }
  67
  68 private template _AliasSeq(TList...) { alias _AliasSeq = TList; }