2. Assert: a proactive programming paractice...

• An assertion declares that a certain condition must be true at a specific point in a program.

• The assertion is said to fail if the condition is false.

• Assertions can tell why errors are happening.

• Assertions can diagnose a problem at the first sign of trouble.

• OK, what should I assert?

  • Short answer: everything!

  • Validate input parameters and check every assumption you made while writing your code.

  • Don't worry that putting in too many assertions degrades program performance: assertions usually active only in debug builds. Bug-finding opportunities outweigh the small performance hit!

  • IMPORTANT: Assertions should never change any variables or program state. Treat all data you check in assertions as read-only.