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Constrained genericity: Difference between revisions
→{{header|Scala}}: ++ sather, hopefully I've taken it right
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(→{{header|Scala}}: ++ sather, hopefully I've taken it right) |
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let your_box = FloatBox.make_box_from_list [2.3; 4.5]</lang>
Unfortunately, it is kind of cumbersome in that, for every type parameter we want to use for this generic type, we will have to explicitly create a module for the resulting type (i.e. <tt>BananaBox</tt>, <tt>FloatBox</tt>). And the operations on that resulting type (i.e. <tt>make_box_from_list</tt>) are tied to each specific module.
=={{header|Sather}}==
<lang sather>abstract class $EDIBLE is
eat;
end;
class FOOD < $EDIBLE is
readonly attr name:STR;
eat is
#OUT + "eating " + self.name + "\n";
end;
create(name:STR):SAME is
res ::= new;
res.name := name;
return res;
end;
end;
class CAR is
readonly attr name:STR;
create(name:STR):SAME is
res ::= new;
res.name := name;
return res;
end;
end;
class FOODBOX{T < $EDIBLE} is
private attr list:LLIST{T};
create:SAME is
res ::= new;
res.list := #;
return res;
end;
add(c :T) is
self.list.insert_back(c);
end;
elt!:T is loop yield self.list.elt!; end; end;
end;
class MAIN is
main is
box ::= #FOODBOX{FOOD}; -- ok
box.add(#FOOD("Banana"));
box.add(#FOOD("Amanita Muscaria"));
box2 ::= #FOODBOX{CAR}; -- not ok
box2.add(#CAR("Punto")); -- but compiler let it pass!
-- eat everything
loop box.elt!.eat; end;
end;
end;</lang>
The GNU Sather compiler v1.2.3 let the "box2" pass, even though it shouldn't. Read e.g. [http://www.gnu.org/software/sather/docs-1.2/tutorial/parameterized1751.html this tutorial's section]
=={{header|Scala}}==
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