在字符串的索引处获取字符

Question

func lengthOfLongestSubstring(s string) {
    match := make(map[string]int)
    var current string

    current = s[0]

    if match[current] == 1 {
        ///
    }

}

Why do I get the error cannot use s[0] (type byte) as type string in assignment? As far as I can tell it's clear that s is of type string, why does accessing a character turn it into type byte?

Answer 1

Let's read how one of the Go designers look at strings in go:

In Go, a string is in effect a read-only slice of bytes. If you're at all uncertain about what a slice of bytes is or how it works, please read the previous blog post; we'll assume here that you have.

It's important to state right up front that a string holds arbitrary bytes. It is not required to hold Unicode text, UTF-8 text, or any other predefined format. As far as the content of a string is concerned, it is exactly equivalent to a slice of bytes.

So, apparently in your case, s[0] is a byte type, you need explicit case if you really need the assignment.