lec07 - CS 3110 Lecture 7 Modular Programming Modules and...

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CS 3110 Lecture 7 Modular Programming: Modules and Signatures We've been building very small programs. When a program is small enough, we can keep all of the details of the program in our heads at once. Real application programs are 100 to 10000 times larger than any program you have likely written or worked on; they are simply too large and complex to hold all their details in our heads. They are also written by multiple authors because otherwise it would take too long. To build large software systems requires techniques we haven't talked about so far. One key solution to managing complexity of large software is modular programming : the code is composed of many different code modules that are developed separately. This allows different developers to take on discrete pieces of the system and design and implement them without having to understand all the rest. However, to build large programs out of modules effectively, we need to be able to write code modules that we can convince ourselves are correct in isolation from the rest of the program. Rather than have to think about every other part of the program when developing a code module, we need to be able to use local reasoning : that is, reasoning about just the module and the contract it needs to satisfy with respect to the rest of the program. If everyone has done their job, separately developed code modules can be plugged together to form a working program without every developer needing to understand everything done by every other developer in the team. This is the idea of modular programming . Therefore, to build large programs that work we must use abstraction to make it manageable to think about the program. Abstraction is simply the removal of detail. A well-written program has the property that we can think about its components (such as functions) abstractly, without concerning ourselves with all the details of how those components are implemented. Modules are abstracted by giving specifications of what they are supposed to do. A good module specification is clear, understandable, and give just enough information about what the module does for clients to successfully use it. This abstraction makes the programmer's job much easier; it is helpful even when there is only one programmer working on a moderately large program, and it is crucial when there is
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This note was uploaded on 10/25/2009 for the course PHYS 2214 at Cornell.

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lec07 - CS 3110 Lecture 7 Modular Programming Modules and...

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