go中的[“”]是什么意思

Question

I see this in the range loop to get a MIME header.

    for _, ext := range parseExtensions(r.Header) {
        if ext[""] != "permessage-deflate" {
            continue
        }
        compress = true
        break
    }

Answer 1

" characters are used to quote strings. So "" is an empty string.

[] is used to reference an element of a map, slice, or array. In your case, it's a map.

So ext[""] is referencing the key of map ext with name "" . Assuming ext is a map with a string key, such as map[string]interface{} or map[string]string , it will work fine. Any other type will result in a compilation error.

Based on context, we can assume that it is a map[string]string , since the value read from the map is being compared to a string.