Swift提供了三種方式來比較文本值：字符串字符相等、前綴相等和后綴相等。

字符串/字符相等

字符串/字符可以用等于操作符（==）和不等于操作符（!=）。

let quotation = "We're a lot alike,you and I."
let sameQuotation = "We're a lot alike,you and I."
if quotation == sameQuotation {
        print("These two strings are considered equal")
}
//打印輸出“These two strings are considered equal”

如果兩個(gè)字符串（或者兩個(gè)字符）的可擴(kuò)展的字形群集是標(biāo)準(zhǔn)相等，那就認(rèn)為它們是相等的。只要可擴(kuò)展的字形群集有同樣的語言意義和外觀則認(rèn)為它們標(biāo)準(zhǔn)相等，即使它們是由不同的 Unicode 標(biāo)量構(gòu)成。

例如，LATIN SMALL LETTER E WITH ACUTE(U+00E9)就是標(biāo)準(zhǔn)相等于LATIN SMALL LETTER E(U+0065)后面加上COMBINING ACUTE ACCENT(U+0301)。這兩個(gè)字符群集都是表示字符é的有效方式，所以它們被認(rèn)為是標(biāo)準(zhǔn)相等的。

//"Voulez-vous un café?"使用LATIN SMALL LETTER E WITH ACUTE
let eAcuteQuestion = "Voulez-vous un caf\u{E9}?"

// "Voulez-vous un café?" 使用 LATIN SMALL LETTER E and COMBINING ACUTE ACCENT
let combinedEAcuteQuestion = "Voulez-vous un caf\u{65}\u{301}?"

if eAcuteQuestion == combinedEAcuteQuestion {
print("These two strings are considered equal")
}
//打印輸出“These two strings are considered equal”

相反，英語中的LATIN CAPITAL LETTER A(U+0041，或者A)不等于俄語中的 CYRILLIC CAPITAL LETTER A(U+0410，或者 A)。兩個(gè)字符看著是一樣的，但卻有不同的語言意義。

let latinCapitalLetterA:Character = "\u{41}"
let cyrillicCapitalLetterA:Character = "\u{0410}"
if latinCapitalLetterA != cyrillicCapitalLetterA {
    print("These two characters are not equivalent")
}
//打印“These two characters are not equivalent”

注：在Swift中，字符串和字符并不區(qū)分地域（not locale-sensitive）。

**前綴/后綴相等**

通過調(diào)用字符串的hasPrefix(_:)/hasSuffix(_:)方法來檢查字符串是否擁有特定前綴/后綴，兩個(gè)方法均接收一個(gè)String類型的參數(shù)，并返回一個(gè)布爾值。

下面的例子以一個(gè)字符串?dāng)?shù)組表示莎士比亞話劇《羅密歐與朱麗葉》中前兩場(chǎng)的場(chǎng)景位置。

let romeoAndJuliet = [
"Act 1 Scene 1: Verona, A public place",
"Act 1 Scene 2: Capulet's mansion",
"Act 1 Scene 3: A room in Capulet's mansion",
"Act 1 Scene 4: A street outside Capulet's mansion",
"Act 1 Scene 5: The Great Hall in Capulet's mansion",
"Act 2 Scene 1: Outside Capulet's mansion",
"Act 2 Scene 2: Capulet's orchard",
"Act 2 Scene 3: Outside Friar Lawrence's cell",
"Act 2 Scene 4: A street in Verona",
"Act 2 Scene 5: Capulet's mansion",
"Act 2 Scene 6: Friar Lawrence's cell"
]

你可以調(diào)用hasPrefix(_:)方法來計(jì)算話劇中第一幕的場(chǎng)景數(shù)：

var act1SceneCount = 0
for scene in romeoAndJuliet {
if scene.hasPrefix("Act 1"){
act1SceneCount += 1
}
}
print("There are (act1SceneCount) scenes in Act 1")
//打印輸出“There are 5 scenes in Act 1”

相似地，你可以用hasSuffix(_:)方法來計(jì)算發(fā)生在不同地方的場(chǎng)景數(shù)。

var mansionCount = 0
var cellCount = 0
for scene in romeoAndJuliet {
if scene.hasSuffix("Capulet's mansion") {
mansionCount += 1
}else if scene.hasSuffix("Friar Lawrence's cell"){
cellCount += 1
}
}
print("(mansionCount) mansion scenes; (cellCount) cell scenes")
//打印輸出“6 mansion scenes; 1 cell scenes”

注：hasPrefix(:)和hasSuffix(:)方法都是在每個(gè)字符串中逐字符比較其可擴(kuò)展的字符群集是否標(biāo)準(zhǔn)相等。