Objective-C中有强类型的集合吗？ [英] Are there strongly-typed collections in Objective-C?

问题描述

我刚刚接触Mac / iPhone编程和Objective-C。在C＃和Java中，我们有泛型，集合类的成员只能是声明的类型。例如，在C＃

I'm new to Mac/iPhone programming and Objective-C. In C# and Java we have "generics", collection classes whose members can only be of the type declared. For example, in C#

字典< int，MyCustomObject>

只能包含整数的键和MyCustomObject类型的值。是否在Objective-C中存在类似的机制？

can only contain keys that are integers and values that are of type MyCustomObject. Does a similar mechanism exist in Objective-C?

推荐答案

在Xcode 7中，Apple引入了轻量级泛型。在Objective-C中，如果存在类型不匹配，它们将生成编译器警告。

In Xcode 7, Apple has introduced 'Lightweight Generics' to Objective-C. In Objective-C, they will generate compiler warnings if there is a type mismatch.

NSArray<NSString*>* arr = @[@"str"];

NSString* string = [arr objectAtIndex:0];
NSNumber* number = [arr objectAtIndex:0]; // Warning: Incompatible pointer types initializing 'NSNumber *' with an expression of type 'NSString *'

在Swift代码中，它们将产生一个编译器错误：

And in Swift code, they will produce a compiler error:

var str: String = arr[0]
var num: Int = arr[0] //Error 'String' is not convertible to 'Int'

轻量级泛型旨在与NSArray，NSDictionary和NSSet一起使用，但也可以将它们添加到您自己的类中：

Lightweight Generics are intended to be used with NSArray, NSDictionary and NSSet, but you can also add them to your own classes:

@interface GenericsTest<__covariant T> : NSObject

-(void)genericMethod:(T)object;

@end

@implementation GenericsTest

-(void)genericMethod:(id)object {}

@end

Objective-C的行为与之前的编译器警告一样。

Objective-C will behave like it did before with compiler warnings.

GenericsTest<NSString*>* test = [GenericsTest new];

[test genericMethod:@"string"];
[test genericMethod:@1]; // Warning: Incompatible pointer types sending 'NSNumber *' to parameter of type 'NSString *'

Swift将完全忽略通用信息。

but Swift will ignore the Generic information completely.

var test = GenericsTest<String>() //Error: Cannot specialize non-generic type 'GenericsTest'

除了这些Foundation集合类， Swift忽略了C的轻量级泛型。使用轻量级泛型的任何其他类型都被导入到Swift中，就像它们未被参数化一样。

Aside from than these Foundation collection classes, Objective-C lightweight generics are ignored by Swift. Any other types using lightweight generics are imported into Swift as if they were unparameterized.

与Objective-C API交互

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