Constrained genericity: Difference between revisions
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Thundergnat (talk | contribs) (Rename Perl 6 -> Raku, alphabetize, minor clean-up) |
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-- We have declared Banana and Tomato as a Food.</lang> |
-- We have declared Banana and Tomato as a Food.</lang> |
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The Tomato_Box can only contain tomatoes; the Banana_Box can only contain bananas. You can only create boxes of eatable objects. |
The Tomato_Box can only contain tomatoes; the Banana_Box can only contain bananas. You can only create boxes of eatable objects. |
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=={{header|C++}}== |
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{{works with|C++11}} |
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Uses static assertion to disallow instantiations on incorrect types |
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<lang c++> |
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template<typename T> //Detection helper struct |
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struct can_eat //Detects presence of non-const member function void eat() |
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{ |
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private: |
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template<typename U, void (U::*)()> struct SFINAE {}; |
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template<typename U> static char Test(SFINAE<U, &U::eat>*); |
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template<typename U> static int Test(...); |
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public: |
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static constexpr bool value = sizeof(Test<T>(0)) == sizeof(char); |
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}; |
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struct potato |
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{ void eat(); }; |
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struct brick |
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{}; |
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template<typename T> |
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class FoodBox |
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{ |
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//Using static assertion to prohibit non-edible types |
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static_assert(can_eat<T>::value, "Only edible items are allowed in foodbox"); |
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//Rest of class definition |
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}; |
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int main() |
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{ |
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FoodBox<potato> lunch; |
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//Following leads to compile-time error |
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//FoodBox<brick> practical_joke; |
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}</lang> |
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=={{header|C sharp|C#}}== |
=={{header|C sharp|C#}}== |
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} |
} |
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} |
} |
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}</lang> |
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=={{header|C++}}== |
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{{works with|C++11}} |
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Uses static assertion to disallow instantiations on incorrect types |
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<lang c++> |
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template<typename T> //Detection helper struct |
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struct can_eat //Detects presence of non-const member function void eat() |
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{ |
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private: |
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template<typename U, void (U::*)()> struct SFINAE {}; |
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template<typename U> static char Test(SFINAE<U, &U::eat>*); |
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template<typename U> static int Test(...); |
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public: |
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static constexpr bool value = sizeof(Test<T>(0)) == sizeof(char); |
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}; |
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struct potato |
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{ void eat(); }; |
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struct brick |
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{}; |
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template<typename T> |
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class FoodBox |
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{ |
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//Using static assertion to prohibit non-edible types |
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static_assert(can_eat<T>::value, "Only edible items are allowed in foodbox"); |
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//Rest of class definition |
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}; |
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int main() |
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{ |
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FoodBox<potato> lunch; |
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//Following leads to compile-time error |
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//FoodBox<brick> practical_joke; |
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}</lang> |
}</lang> |
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nom..nom..nom |
nom..nom..nom |
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nom..nom..nom</pre> |
nom..nom..nom</pre> |
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=={{header|Nim}}== |
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<lang nim>type |
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Eatable = concept e |
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eat(e) |
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FoodBox[e: Eatable] = seq[e] |
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Food = object |
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name: string |
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count: int |
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proc eat(x: int) = echo "Eating the int: ", x |
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proc eat(x: Food) = echo "Eating ", x.count, " ", x.name, "s" |
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var ints = FoodBox[int](@[1,2,3,4,5]) |
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var fs = FoodBox[Food](@[]) |
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fs.add Food(name: "Hamburger", count: 3) |
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fs.add Food(name: "Cheeseburger", count: 5) |
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for f in fs: |
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eat(f)</lang> |
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=={{header|Objeck}}== |
=={{header|Objeck}}== |
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} |
} |
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}</lang> |
}</lang> |
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=={{header|Nim}}== |
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<lang nim>type |
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Eatable = concept e |
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eat(e) |
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FoodBox[e: Eatable] = seq[e] |
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Food = object |
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name: string |
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count: int |
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proc eat(x: int) = echo "Eating the int: ", x |
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proc eat(x: Food) = echo "Eating ", x.count, " ", x.name, "s" |
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var ints = FoodBox[int](@[1,2,3,4,5]) |
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var fs = FoodBox[Food](@[]) |
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fs.add Food(name: "Hamburger", count: 3) |
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fs.add Food(name: "Cheeseburger", count: 5) |
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for f in fs: |
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eat(f)</lang> |
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=={{header|Objective-C}}== |
=={{header|Objective-C}}== |
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print MrG.WeightGain 'result 15.75 |
print MrG.WeightGain 'result 15.75 |
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</lang> |
</lang> |
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=={{header|Perl 6}}== |
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{{works with|Rakudo|2016.01}} |
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<lang perl6>subset Eatable of Any where { .^can('eat') }; |
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class Cake { method eat() {...} } |
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role FoodBox[Eatable] { |
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has %.foodbox; |
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} |
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class Yummy does FoodBox[Cake] { } # composes correctly |
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# class Yucky does FoodBox[Int] { } # fails to compose |
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my Yummy $foodbox .= new; |
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say $foodbox.perl;</lang> |
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{{out}} |
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<lang>Yummy.new(foodbox => {})</lang> |
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=={{header|Phix}}== |
=={{header|Phix}}== |
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All the tests pass. Look at the tests to see what generates an exception (i.e. |
All the tests pass. Look at the tests to see what generates an exception (i.e. |
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not allowed at runtime) and what does not. |
not allowed at runtime) and what does not. |
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=={{header|Raku}}== |
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(formerly Perl 6) |
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{{works with|Rakudo|2016.01}} |
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<lang perl6>subset Eatable of Any where { .^can('eat') }; |
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class Cake { method eat() {...} } |
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role FoodBox[Eatable] { |
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has %.foodbox; |
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} |
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class Yummy does FoodBox[Cake] { } # composes correctly |
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# class Yucky does FoodBox[Int] { } # fails to compose |
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my Yummy $foodbox .= new; |
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say $foodbox.perl;</lang> |
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{{out}} |
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<lang>Yummy.new(foodbox => {})</lang> |
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=={{header|Ruby}}== |
=={{header|Ruby}}== |
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