Another update from ingydotnet^djgoku

Task/Constrained-genericity/C++/constrained-genericity.cpp

@@ -0,0 +1,33 @@
+template<typename T> //Detection helper struct
+struct can_eat       //Detects presence of non-const member function void eat()
+{
+  private:
+    template<typename U, void (U::*)()> struct SFINAE {};
+    template<typename U> static char Test(SFINAE<U, &U::eat>*);
+    template<typename U> static int Test(...);
+  public:
+    static constexpr bool value = sizeof(Test<T>(0)) == sizeof(char);
+};
+
+struct potato
+{ void eat(); };
+
+struct brick
+{};
+
+template<typename T>
+class FoodBox
+{
+    //Using static assertion to prohibit non-edible types
+    static_assert(can_eat<T>::value, "Only edible items are allowed in foodbox");
+
+    //Rest of class definition
+};
+
+int main()
+{
+    FoodBox<potato> lunch;
+
+    //Following leads to compile-time error
+    //FoodBox<brick> practical_joke;
+}

Task/Constrained-genericity/Forth/constrained-genericity.fth

@@ -0,0 +1,61 @@
+include FMS-SI.f
+include FMS-SILib.f
+
+: (where) ( class-xt where-dfa -- flag )
+     swap >body { where-dfa class-dfa }
+     begin
+       class-dfa ['] object >body <>
+     while
+       class-dfa where-dfa = if true exit then
+       class-dfa sfa @  to class-dfa
+     repeat false ;
+
+: where ( class-xt "classname" -- flag )
+  ' >body state @
+  if postpone literal postpone (where)
+  else (where)
+  then ; immediate
+
+:class Eatable
+   :m eat cr ." successful eat" ;m
+;class
+
+\ FoodBox is defined without using eat in any way.
+:class FoodBox
+  object-list eatable-types
+  :m fill: { n class-xt -- }
+     class-xt where Eatable
+     if   n 0 do class-xt eatable-types xtadd: loop
+     else ." not an eatable type "
+     then ;m
+  :m get ( -- obj ) eatable-types ;m
+;class
+
+: test ( obj -- )  \ send the eat message to each object in the object-list
+  begin dup each:
+  while eat
+  repeat drop ;
+
+FoodBox fb
+3 ' Eatable fb fill:  \ fill the object-list with 3 objects of class Eatable
+fb get test
+successful eat
+successful eat
+successful eat
+
+FoodBox fb1
+5 ' object fb1 fill: \ => not an eatable type
+
+:class apple <super Eatable
+;class
+
+:class green-apple <super apple
+;class
+
+5 ' green-apple fb1 fill:
+fb1 get test
+successful eat
+successful eat
+successful eat
+successful eat
+successful eat

Task/Constrained-genericity/Objective-C/constrained-genericity-1.m

@@ -0,0 +1,3 @@
+@protocol Eatable
+- (void)eat;
+@end

Task/Constrained-genericity/Objective-C/constrained-genericity-2.m

@@ -0,0 +1,2 @@
+@interface FoodBox<T : id<Eatable>> : NSObject
+@end