rangerdanger

Install:

    go get [-u] github.com/mdempsky/rangerdanger

Usage:

    rangerdanger std cmd

Description:

    In go, an array is not a reference type (that's what slices are for). An array is a value type,
    which means the entire thing is copied in some circumstances such as assigning it to a new variable
    or passing the array as a function argument. For more details see:

    https://blog.golang.org/go-slices-usage-and-internals

    A somewhat surprising consequence is that when using the two-valued "range" clause to iterate over
    an array, you end up making a copy of the array. The compiler does this to adhere to the specified
    semantics of "range" - namely that the provided expression is evaluated once only. This means that
    any changes made to the array contents do not affect the iteration in progress. In many cases you'd
    rather give up that guarantee than copy the whole array; rangerdanger exists to detect uses of
    "range" which result in an array copy so they can be avoided when desired.

Example:

    import "fmt"
    
    func main() {
        array := [...]int{1,4,9,16,25}
        
        // this usage of range makes a copy of the array
        for i, n := range array {
            // reverse the array and turn square numbers into cube numbers
            array[len(array) - 1 - i] = n
        }
        fmt.Println(array) // prints [25 16 9 4 1]

        // to avoid copying the array, pass a slice instead
        for i, n := range array[:] {
            // attempt to reverse the array again
            array[len(array) - 1 - i] = n
        }
        fmt.Println(array) // prints [25 16 9 16 25]
    }