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CLU is a pioneering programming language created at MIT by Barbara Liskov and her students between 1974 and 1975. While it did not find extensive use itself, it introduced many features that are now widely used, and is seen as a step in the development of object-oriented programming (OOP). However, it is not object-oriented itself, instead being considered "object-based", as it lacked many features of OOP. Key contributions include abstract data types, call-by-sharing, iterators, multiple return values (a form of parallel assignment), type-safe parameterized types, and type-safe variant types. It is also notable for its use of classes with constructors and methods, but without inheritance. == Clusters == The syntax of CLU was based on ALGOL, then the starting point for most new language designs. The key addition was the concept of a ''cluster'', CLU's type extension system and the root of the language's name (CLUster). Clusters correspond generally to the concept of an "class" in an OO language, and have similar syntax. For instance, here is the CLU syntax for a cluster that implements complex numbers: complex_number = cluster is add, subtract, multiply, ... rep = record (real_part: real, imag_part: real ) add = proc ... end add; subtract = proc ... end subtract; multiply = proc ... end multiply; ... end complex_number; A cluster is a module that encapsulates all of its components except for those explicitly named in the "is" clause. These correspond to the public components of a class in recent OO languages. A cluster also defines a type that can be named outside the cluster (in this case, "complex_number"), but its representation type (rep) is hidden from external clients. Cluster names are global, and no namespace mechanism was provided to group clusters or allow them to be created "locally" inside other clusters. CLU does not perform implicit type conversions. In a cluster, the explicit type conversions 'up' and 'down' change between the abstract type and the representation. There is a universal type 'any', and a procedure force[] to check that an object is a certain type. Objects may be mutable or immutable, the latter being "base types" such as integers, booleans, characters and strings.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「CLU (programming language)」の詳細全文を読む スポンサード リンク
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