Default case in select in Go - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of the default case in a Go select statement?

The default case runs immediately if no other case in the select is ready. It prevents the select from blocking and allows the program to continue.

beginner

Can a select statement in Go block if it has a default case?

No. If a select has a default case, it will never block. It will run the default immediately if no other channel operation is ready.

intermediate

What happens if multiple channel operations in a select are ready at the same time?

Go picks one of the ready cases at random to run. If there is a default case, it only runs if no other case is ready.

beginner

Write a simple Go select statement with a default case that prints "No message received" if no channel is ready.

select { case msg := <-ch: fmt.Println("Received:", msg) default: fmt.Println("No message received") }

intermediate

Why might you use a default case in a select statement in Go?

To avoid blocking when waiting on channels, allowing the program to do other work or check conditions repeatedly without getting stuck.

What does the default case in a Go select statement do?

A Blocks until a channel is ready

B Runs immediately if no other case is ready

C Closes all channels

D Terminates the program

The default case runs immediately if no other channel operation is ready, preventing blocking.

If a select statement has a default case, can it ever block?

A No, never

B Yes, always

C Only if channels are closed

D Only if the default case is empty

Having a default case means the select will never block; it runs the default immediately if no other case is ready.

What happens if multiple channel cases in a select are ready at the same time?

A The program panics

B The first case is always chosen

C One case is chosen at random

D The default case runs

Go randomly picks one of the ready cases to run when multiple are ready.

Which of these is a reason to use a default case in a select?

A To close channels automatically

B To wait indefinitely for a message

C To restart the program

D To avoid blocking when no channels are ready

The default case lets the program continue without blocking if no channels are ready.

What will this code print if channel ch has no message ready?

select {
case msg := <-ch:
    fmt.Println(msg)
default:
    fmt.Println("No message")
}

A It prints "No message"

B It prints the message from ch

C It blocks forever

D It causes a runtime error

Since ch has no message ready, the default case runs and prints "No message".

Explain how the default case works in a Go select statement and why it is useful.

Think about what happens when no channels are ready to send or receive.

Write a Go select statement with a default case that handles receiving from a channel and prints a message if no data is available.

Use <code>select</code> with a receive case and a <code>default</code> that prints.