Use of variable in 'for' loop is not recognized in Go

Question

I'm developing in Go and I run the following for loop:

// Define Initial Value
i := 0

for {
    // Get random data based on iteration
    data, i := GiveRandomData(i)

    // Save to database
    response, err := SaveToDatabase(data)

    if err != nil { log.Fatal(err) }
    fmt.Println(response)
}

However, when compiling this program, I get the following error:

.\main.go:26: i declared and not used

The Go compiler doesn't seem to recognise that the i variable is given back to the function in the next loop. Inside this function, the I variable changes value.

What should I do to get rid of this compilation error or to let Go understand that this variable is not unused, but used in the next iteration of this endless for loop?

2 revs, 2 users 83% · Accepted Answer · 2022-05-23 13:42:19Z

9

The Go compiler doesn't seem to recognise that the i variable is given back to the function in the next loop. Inside this function, the I variable changes value.

No, i does not change value; := declares a new i. (Go allows you to do this because data is also new.) To assign to it instead, you’ll need to declare data separately:

var data RandomDataType
data, i = GiveRandomData(i)

Or give the new i a temporary name:

data, next := GiveRandomData(i)
i = next

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