Swift学习笔记

1. 不可变字符串

Objective-C:

NSString *string1 = @"Hello World!";

Swift:

let string1 = "Hello world!"

2. 可变字符串

Objective-C:

NSMutableString *string2 = [NSMutableString new];
NSMutableString *string3 = [@"" mutableCopy];

Swift:

var string2 = String()
var string3 = ""

3. 输出

Objective-C:

NSLog(@"%lu", (unsigned long)string1.length); // Prints "12"
NSLog(@"%i", !string2.length);                 // Prints "1"
NSLog(@"%i", [string1 hasPrefix:@"Hello"]); // Prints "1"
NSLog(@"%i", [string1 hasSuffix:@"earth!"]);// Prints "0"

Swift:

println(string1.utf16Count)                // Prints "12"
println(countElements(string1))            // Prints "12"
println(string2.isEmpty)                // Prints "true"
println(string1.hasPrefix("Hello"))     // Prints true
println(string1.hasSuffix("earth!"))     // Prints false

4. 比较

Objective-C:

// Prints "string2 equals string3"
if ([string2 isEqualToString:string3]) {
    NSLog(@"string2 equals string3");
}

Swift:

// Prints "string2 equals string3"
if string2 == string3 {
    println("string2 equals string3")
}

5. 转换

Objective-C:

NSString *fiveString = [@5 stringValue]; // "5"
NSInteger five = [fiveString integerValue];

Swift:

let fiveString = "(5)"                         // "5"
let five = fiveString.toInt()!
let pi = Double((π as NSString).doubleValue)     // 3.14

6. Copy and Mutable Copy

Objective-C:

NSMutableString *string4 = [string1 mutableCopy];
[string4 appendFormat:@"Am I alone?"];
NSLog(@"%@", string1);        // Prints "Hello world!"
NSLog(@"%@", string4);        // Prints "Hello world! Am I alone?"
NSMutableString *string5 = string4;
[string5 replaceCharactersInRange:NSMakeRange(13, 10)
    withString:@"How do you like me now"];
// Prints "Hello world! How do you like me now?"
if ([string4 isEqualToString:string5]) {
    NSLog(@"%@", string5);
}

NSMutableString *tempHigh = [@"85" mutableCopy];
NSMutableString *tempLow = [@"70" mutableCopy];
NSString *degreeF = @"u2109";
[tempHigh appendString:degreeF];
[tempLow appendString:degreeF];

// Prints "High/Low: 85°F/70°F"
NSLog(@"High/Low: %@/%@", tempHigh, tempLow); 

Swift:

var string4 = string1
string4 += " Am I alone?"
println(string1)         // Prints "Hello world!"
println(string4)         // Prints "Hello world! Am I alone?"
var string5 = string4
let startIndex = advance(string5.startIndex, 13)
string5.replaceRange(startIndex..<string5.endIndex, with: "How do you like me now?")
// Prints "Hello world! How do you like me now?"
if string4 != string5 {
    println(string5)
}


var tempHigh = "85"
var tempLow = "70"
let degreeF: Character = "u{2109}"
tempHigh.append(degreeF)
tempLow.append("u{2109}" as Character)
// Prints "High/Low: 85°F/70°F"
println("High/Low: (tempHigh)/(tempLow)")