Introduction Essays (4231 words) - Object-oriented Programming

Introduction -------------------------------------------------------------------------------- Sather is an object oriented language designed to be simple, efficient, safe, and non-proprietary. It aims to meet the needs of modern research groups and to foster the development of a large, freely available, high-quality library of efficient well-written classes for a wide variety of computational tasks. It was originally based on Eiffel but now incorporates ideas and approaches from several languages. One way of placing it in the 'space of languages' is to say that it attempts to be as efficient as C, C++, or Fortran, as elegant but safer than Eiffel or CLU, and to support higher-order functions as well as Common Lisp, Scheme, or Smalltalk. Sather has garbage collection, statically-checked strong (contravariant) typing, multiple inheritance, separate implementation and type inheritance, parameterized classes, dynamic dispatch, iteration abstraction, higher-order routines and iters, exception handling, assertions, preconditions, postconditions, and class invariants. Sather code can be compiled into C code and can efficiently link with object files of other languages. pSather, the parallel and distributed extension, presents a shared memory abstraction to the programmer while allowing explicit placement of data and threads. Sather and the ICSI Sather compiler have a very unrestrictive license aimed at encouraging contribution to the public library without precluding the use of Sather for proprietary projects. This chapter will provide a basic introduction for new users, pointing to sources of information about the language and the compiler. It also contains a summary of Sather features - for those familiar with another object-oriented language, this section provides an overview of the key features of Sather. 1.1 Acknowledgements This text has its roots in the Sather 1.1 specification, the Eclectic tutorial and Holger's iterator tutorial. This document also contains several organizational ideas and some text from S. Omohundro's originally planned Sather book. This text has benefitted from corrections, comments and suggestions from several people including Cary D. Renzema, Jerome Feldman, Claudio Fleiner and Arno Jacobsen. Particular thanks to Cary, Arno and Feldman for detailed error reports. Arno also made several suggestions regarding terminology and examples that have been incorporated. 1.2 How to read this Document This document is meant to be a complete description of Sather 1.1, and is intended as an introduction to the language for a person with some programming background. It is more expository in nature than the specification and contains sections that motivate particular aspects of the language, such as the overloading rules. In addition, it deals with some more abstract design issues that arise when programming in Sather (such as the effect of the contra-variant subtyping rule). 1.3 Sources of Information This section briefly introduces some concepts important to Sather that the reader may not have been exposed to in C++ [2]. It isn't meant as a complete language tutorial. More information of a tutorial nature is available from the WWW page: http://www.icsi.berkeley.edu/Sather At the time of this writing, the only compiler implementing the 1.1 language specification is available from ICSI. It is freely available, includes source for class libraries and the compiler, and compiles into ANSI C. This compiler has been ported to a wide range of UNIX and PC operating systems. 1.4 Obtaining the Compiler The ICSI Sather 1.1 compiler can be obtained by anonymous ftp at ftp.icsi.berkeley.edu: /pub/sather Other sites also mirror the Sather distribution. The distribution includes installation instructions, 'man' pages, the standard libraries and source for the compiler (in Sather). Documentation, tutorials and up-to-date information are also available at the Sather WWW page: http://www.icsi.berkeley.edu/~sather ICSI also maintains a library of contributed Sather code at this page. There is a newsgroup devoted to Sather: comp.lang.sather There is also a Sather mailing list if you wish to be informed of Sather releases; to subscribe, send email to: [emailprotected] It is not necessary to be on the mailing list if you read the Sather newsgroup. 1.4.1 How do I ask questions? If it appears to be a problem that others would have encountered (on platform 'X', I tried to install it but the it failed to link with the error 'Y'), then the newsgroup is a good place to ask. If you have problems with the compiler or questions that are not of general interest, mail to one of [emailprotected] [emailprotected] This is also where you want to send bug reports. 1.5 Summary of Features This section provides a summary of Sather's features, with particular attention to features that are not found in