A default case makes a select statement non-blocking. When no channel operation is ready, its instructions run immediately, allowing the current execution to do other work instead of waiting. section 8.1.2
Polling for a delayed message
A loop can repeatedly try to receive a message while the default case reports that nothing is waiting. After the delayed sender transmits "Hello", the receive case runs and the program returns. Adding a short sleep prevents the loop from repeatedly printing without pause. section 8.1.2
The same pattern can coordinate concurrent work:
- Place computation under default so a goroutine continues processing when no stop signal is available. section 8.1.3
- Use a shared stop channel as the other case; when one goroutine closes it, the remaining goroutines detect the signal and return. section 8.1.3
