Presentation November 2 nd , 2009 Quoc K. Le CS 265- 001

1. Presentation November 2nd, 2009 Quoc K. Le CS 265- 001

2. A summary of interface principles

3. Interface • Interface is the detailed boundary between code that provides a service and code that uses it. • It defines: What some body of code does for its users, how functions can be used

4. Generally, good interfaces must follow a set of principles: • Hide implementation details (Info hiding) • Choose a small orthogonal set of primitives • Don’t do secret stuffs. • Be consistent

5. Hide implementation details: Other terms for this kind of organizing principle: Encapsulation, Information hiding, abstraction, modulization. Example: Classes such as string, vector, deque… It’s easy to implement them without knowing how they do

6. It’s recommendable not to make data publicly visible. • Users might change variables.

7. 2. Choose a small orthogonal set of primitives. • An interface should provide as much functionality as necessary but no more. • A large interface is harder to build and maintain. • It also makes users harder to learn. • Narrow interface are preferred.

8. Example: C standard I/O library provides several ways to write a single character to an output stream: • char c; • putc(c, fp); • fputc(c, fp); Not necessary!

9. 3. Don’t be secret • A library function should not write secret files and variables or change global data • Example: function strtok in the class string It functions to split string into tokens. However the function writes NULL bytes into the middle of its input string

11. 4. Consistency: In other words, do the same thing the same way everywhere. Consistency makes functions easy to understand and use without much studying. Example: The loops are presented quite the same ways in several languages such as C++, Java, Perl…