Objective-C和Swift的转换速查手册（推荐）

//Swift
let username = "twostraws"
print("Username is (username)")

控制流

检查状态

//Objective-C
NSInteger result = 86;
if (result >= 85) {
 NSLog(@"You passed the test!");
} else {
 NSLog(@"Please try again.");
}

//Swift
let result = 86

if result >= 85 {
 print("You passed the test!")
} else {
 print("Please try again.")
}

循环一定次数

//Objective-C
for (NSInteger i = 0; i < 100; ++i) {
 NSLog(@"This will be printed 100 times.");
}

//Swift
for _ in 0 ..< 100 {
 print("This will be printed 100 times.")
}

在数组中循环

//Objective-C
NSArray *companies = @[@"Apple", @"Facebook", @"Twitter"];

for (NSString *name in companies) {
 NSLog(@"%@ is a well-known tech company.", name);
}

//Swift
let companies = ["Apple", "Facebook", "Twitter"]

for name in companies {
 print("(name) is a well-known tech company.")
}

数值切换

//Objective-C
NSInteger rating = 8;

switch (rating) {
 case 0 ... 3:
 NSLog(@"Awful");
 break;
 case 4 ... 7:
 NSLog(@"OK");
 break;
 case 8 ... 10:
 NSLog(@"Good");
 break;
 default:
 NSLog(@"Invalid rating.");
}
//很多人不知道Objective-C有范围支持，所以你也许看到二选一的语法

//Swift
let rating = 8

switch rating {
case 0...3:
 print("Awful")
case 4...7:
 print("OK")
case 8...10:
 print("Good")
default:
 print("Invalid rating.")
}
//Swift不会fall through案例，除非你使用fallthrough关键字

函数

不接收参数也没有返回的函数