檢查並比較字串

檢查字串是否為空：

if str.isEmpty {
    // do something if the string is empty
}

// If the string is empty, replace it with a fallback:
let result = str.isEmpty ? "fallback string" : str

檢查兩個字串是否相等（在 Unicode 規範等價意義上 ）：

"abc" == "def"          // false
"abc" == "ABC"          // false
"abc" == "abc"          // true

// "LATIN SMALL LETTER A WITH ACUTE" == "LATIN SMALL LETTER A" + "COMBINING ACUTE ACCENT"
"\u{e1}" == "a\u{301}"  // true

檢查字串是否以另一個字串開頭/結尾：

"fortitude".hasPrefix("fort")      // true
"Swift Language".hasSuffix("age")  // true