Fan-in in Go

Merging several channels into one, closing the result when all are done.

func merge(inputs ...<-chan int) <-chan int {
    out := make(chan int)
    var wg sync.WaitGroup

    for _, input := range inputs {
        wg.Go(func() {
            for value := range input {
                out <- value
            }
        })
    }

    go func() {
        wg.Wait()
        close(out)
    }()
    return out
}

How it works

1. A goroutine per input copies into the shared output.
2. A WaitGroup decides when it is safe to close the output.
3. The closing goroutine must not be one of the copiers.

Keywords and builtins used here

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

The run, in numbers

Lines

18

Characters to type

234

Tokens

74

Three-star pace

110 tpm

At the three-star pace of 110 tokens a minute, this run takes about 40 seconds.

Type this snippet

Step 3 of 5 in Patterns, step 21 of 25 in Concurrency.

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