测试索引超出范围golang

Question

Sorry for this noob question, but I'm not sure how I test to see if an element I'm accessing is valid for an array, consider the following contrived code:

func main() {
    strings := []string{"abc", "def", "ghi", "jkl"}
    for i := 0; i<5; i++ {
        if strings[i] {
            fmt.Println(strings[i])
        }
    }
}

https://play.golang.org/p/8QjGadu6Fu

I'm obviously going outside of the bounds, but I'm not sure how I test to prevent the error. I'm used to PHP where I would use an isset or !empty test, does go have such a thing?

I've browsed other questions and seen the len function used, but that doesn't appear to work.

Answer 1

In Go, this is not quite as easy as in PHP - but keep in mind that in PHP it's only easy because "indexed" arrays are actually associative arrays under the hood. Otherwise you wouldn't be able to "punch holes" into arrays by unsetting individual elements.

With Go arrays/slices, you have to actually check against the length of the array, as you wrote:

if i>=0 && i<len(strings) {...}

Personally, I've yet to come across a real life situation that requires doing this - in your example, you could use range(strings) and stop worrying about indexes.

With maps, which are the Go equivalent of PHP arrays, you can do "isset" by writing:

value, isset := map[index]

if index is present in the map, value will be set appropriately and isset will be true; if not, value will be set to the zero value of the map's type and isset will be false.