4.4 Implicit Type Parameters in Extension Declarations

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4 Parameterization and Parametric Polymorphism

4.4 Implicit Type Parameters in Extension Declarations

An extension declaration can augment either an instance of a parameterized type or a collection of instances using an implicit type parameter. For example, the following declaration extends a single instance of a parameterized type:

extend array[char] subtypes string;

and the following declaration extends a collection of related types:

extend collection['T <= printable] isa printable;

To extend a parameterized type itself, not just some instances, an extension declaration that updates all instances is used:

extend list['T] subtypes variable_length_collection[T];

The Cecil Language: Specification and Rationale, Version 2.1 - 25 MARCH 1997

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