Channel direction in Go

A parameter type can restrict a channel to sending or receiving.

func produce(out chan<- int, count int) {
    for i := 1; i <= count; i++ {
        out <- i * i
    }
    close(out)
}

func consume(in <-chan int) int {
    total := 0
    for value := range in {
        total += value
    }
    return total
}

func pipeline() int {
    numbers := make(chan int)
    go produce(numbers, 4)
    return consume(numbers)
}

How it works

1. chan<- T only sends, <-chan T only receives.
2. The compiler enforces it, so a producer cannot read its own output.
3. Only the sender should close, which the types make obvious.

Keywords and builtins used here

• chan
• close
• for
• func
• go
• int
• make
• range
• return

The run, in numbers

Lines

20

Characters to type

299

Tokens

87

Three-star pace

100 tpm

At the three-star pace of 100 tokens a minute, this run takes about 52 seconds.

Type this snippet

Step 4 of 4 in Channels, step 7 of 25 in Concurrency.

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