Range

The keyword range can be used for loops. It can loopover slices, arrays, strings, maps and channels (see ). range is aniterator that, when called, returns the next key-value pair from the “thing” itloops over. Depending on what that is, range returns different things.

When looping over a slice or array, range returns the index in the slice asthe key and value belonging to that index. Consider this code:

list := []string{"a", "b", "c", "d", "e", "f"}
for k, v := range list {
    // do something with k and v
}

First we create a slice of strings. Then we use range to loop over them. Witheach iteration, range will return the index as an int and the key asa string. It will start with 0 and “a”, so k will be 0 through 5, and v willbe “a” through “f”.

You can also use range on strings directly. Then it will break out theindividual Unicode characters ^[In the UTF-8 world characters are sometimescalled runes Mostly, when people talk about characters, theymean 8 bit characters. As UTF-8 characters may be up to 32 bits the word rune isused. In this case the type of char is rune. and their start position, byparsing the UTF-8. The loop:

for pos, char := range "Gő!" {
    fmt.Printf("character '%c' starts at byte position %d\n", char, pos)
}

prints

character 'G' starts at byte position 0
character 'ő' starts at byte position 1
character '!' starts at byte position 3

Note that ő took 2 bytes, so ‘!’ starts at byte 3.