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The standard output is three lines:This is program output, excluding any interactive interpreter's display of returned values. The calls a.m(1) and b.m(5.6) compute squares without printing. In A, the concrete m(Int) wins over the generic method at argument 1; the string and 2.3 use m[T] and print their arguments.

For b: B[Any], the class type parameter has already become Any, so the two alternatives are m(Any) and m(Double), rather than a method with its own freely inferred type parameter. The Double alternative is more specific. It accepts 4 by numeric widening, so b.m(4) computes 16.0 without printing; b.m("B") prints B; b.m(5.6) computes a square without printing. These are applications of the Scala 2.11 method overloading rules, with the arithmetic return values discarded in statement position.^[ref]

Two mechanisms are subtype polymorphism and parametric polymorphism.

With subtype polymorphism, a trait or abstract class declares an operation and concrete subclasses implement or override it. A Player reference holding a House object invokes House.play through dynamic dispatch. The client is written against the common contract.

With parametric polymorphism, a software class or generic method has a type parameter, such as List[T] or def identity[T](x: T): T = x. The same definition works for many supplied type arguments, with static relationships between input and output types. Method overloading is another mechanism, usually called ad hoc polymorphism: alternatives share a name but are selected from their parameter signatures at compile time.