Swift：比较字符串的第一个字符

Question

How can I compare the first character of a String against a character in Swift? For example:

Pseudo code:

str = "my name is John"

if str[0] == m {
} 

Answer 1

let s = "abcd"

if s.hasPrefix("a") {  // takes a String or a literal
}

if s.first == "a" {  // takes a Character or a literal
}

if s[s.startIndex] == "a" { // takes a Character or a literal
}

Answer 2

This is for any charactor comparision in Swift 3 :

    var str: String = "abcd"    

    if str[str.index(str.startIndex, offsetBy: i)] == "a" {

    }

where, i = use any index value of string In above example it is 0 i = 0