When should a channel carry 'chan struct{}' versus a typed value, and why is close() used for broadcast?

chan struct{} is the Go idiom for pure signalling — when the fact that something occurred matters, but no data needs to be transferred. struct{}{} has zero size (no memory allocated for the value), and using it explicitly communicates 'this is a signal only'.

// chan struct{} — pure event signal (no payload)
done := make(chan struct{})
go func() {
    doWork()
    close(done) // broadcast: no value needed
}()
<-done // wait for signal

// Buffered chan struct{} as semaphore (acquire/release)
sem := make(chan struct{}, 10)
sem <- struct{}{}   // acquire
<-sem               // release

// chan bool — avoid for signals (true vs false ambiguity)
// What does 'false' mean? Failure? Not-yet? Done? Confusing.

// chan T — use when data has semantic meaning
results := make(chan int, 100)  // carries computed results
errors  := make(chan error, 10) // carries error values

// Broadcast via close: O(1), unblocks ALL receivers
ready := make(chan struct{})
go func() {
    initialize()
    close(ready) // all waiting goroutines unblock simultaneously
}()

for i := 0; i < 5; i++ {
    go func() {
        <-ready      // all 5 unblock at the instant close() is called
        doPostInit()
    }()
}

// struct{} size verification
fmt.Println(unsafe.Sizeof(struct{}{})) // 0 bytes

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