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Polymorphism: Difference between revisions
Added Prolog
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print(instance1);
print(instance2);</lang>
=={{header|Prolog}}==
Prolog is not object oriented but polymorphic behaviour is easy to reproduce by replicating predicates for different types.
'classes' are represented by terms (eg: point(x,y), cicle(x,y,z)).
The Copy constructor, assignment and destructor operations are not needed as terms can be copied and assigned using unification as part of the language.
<lang prolog>% Point
point_construct(X, Y, point(X1,Y1)) :-
default(X, X1),
default(Y, Y1).
% Circle
circle_construct(X, Y, R, circle(X1,Y1,R1)) :-
default(X, X1),
default(Y, Y1),
default(R, R1).
% Accessors for general X,Y
% individual getters/setters can be made but it is not required
shape_x_y_set(point(_,_), X, Y, point(X,Y)).
shape_x_y_set(circle(_,_,R), X, Y, circle(X,Y,R)).
% Accessors for R
cicle_r_set(circle(X,Y,_), R, circle(X,Y,R)).
% Print
print_shape(point(X,Y)) :- format('Point (~p,~p)', [X,Y]).
print_shape(circle(X,Y,R)) :- format('Circle (~p,~p,~p)', [X,Y,R]).
% Default values for constructor (default to 0).
default(N, 0) :- var(N).
default(N, N) :- number(N).
% Tests
test_point :-
point_construct(2,3,P),
test_poly(P).
test_circle :-
circle_construct(3,4,_,C),
cicle_r_set(C, 5, C1),
test_poly(C1).
test_poly(T) :-
shape_x_y_set(_, X, Y, T),
X1 is X * 2,
Y1 is Y * 2,
shape_x_y_set(T, X1, Y1, T1),
print_shape(T1).</lang>
{{out}}
<pre>
?- test_point, nl, test_circle, !.
Point (4,6)
Circle (6,8,5)
true.
?-
</pre>
=={{header|PureBasic}}==
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