Objective-C泛型不工作的方法？ （Xcode 7 Beta（build：7A120f））

问题描述

所以，很明显，在WWDC之后我在玩上周的新东西。正如你所知苹果向Objective-C的世界引入泛型

我在方法中尝试过这个代码，效果非常好

  NSMutableArray< NSString *> * array = [[NSMutableArray alloc] init]; 
 
 [array addObject：@]; 
 [array addObject：@（54）];不兼容的指针类型发送'NSNumber *'到类型'NSString * __nonnull'的参数
 //很好，泛型像预期的一样工作。但是我也有方法转换为泛型
 
 $ b 
 
 
 $ b 
在标题文件中：
   - （NSArray< NSString *> *）objectsToSearch;实施：
  
 code>  - （NSArray< NSString *> *）objectsToSearch 
 {
 NSString * first = @1 
 
 NSString * second = @2; 
 
 NSString * third = @3; 
 
 NSNumber * test = @（55）; 
 
 return @ [first，second，third，test]; //无错误！ 
} 
  
我做错了事或Clang不支持泛型+文字， 
解决方案
我刚刚诊断了这一点，我不认为这是一个错误。以下代码显示了各种选项以及为什么每个都将编译或不编译。 注意：这是基于我的猜测，如何工作。  
  #pragma clang诊断推送
 #pragma clang diagnostic ignored-Wunused-variable
  - （void）testGenericArrays {
 
 NSString * aString = @abc; 
 NSNumber * aNumber = @（55）; 
 
 NSArray< NSString *> * arr1 = @ [aString，aNumber]; 
 //编译，因为RHS在编译时是一个非类型数组。 
 
 NSArray< NSString *> * arr2 = @ [aString，@（20）]; 
 //编译，因为RHS在编译时是一个非类型数组。 
 
 NSArray< NSString *> * arr3 = [NSArray< NSString *> arrayWithObjects：aString，aNumber，@（20），nil]; 
 //编译，因为arrayWithObjects的类型擦除只键入第一个参数，它是一个NSString。 
 //其余的参数是一个vaList，在头处理期间不检查。 
 
 NSArray< NSString *> * arr4 = [NSArray< NSString *> arrayWithObjects：@（20），nil]; //<  -  Error！ 
 NSArray< NSString *> * arr5 = [NSArray< NSString *> arrayWithObjects：aNumber，nil]; //<  -  Error！ 
 //这两个都不编译，因为第一个参数现在是NSNumber并且被检查。 
 
 NSArray< NSString *> * arr6 = [NSArray< NSString *> arrayWithObject：aNumber]; //<  -  Error！ 
 //不会编译，因为在头处理期间检查了参数。 
 
 NSArray< NSString *> * arr7 = [NSArray arrayWithObject：aNumber]; 
 //编译，因为RHS在编译时是一个非类型数组。 
 
 NSMutableArray< NSString *> * arr8 = [[NSMutableArray alloc] init]; 
 [arr8 addObject：aNumber]; //<  -  Error！ 
 //不编译，因为LHS是一个类型数组，我们正在添加它。 
} 
 #pragma clang诊断pop 
  
随意剪切和粘贴到单元测试，并自己尝试。
 
So, obviously, after WWDC I'm playing with new stuff presented during last week. As you know Apple introduced generics to the world of Objective-C
I tried this code in method, works great
NSMutableArray<NSString*> *array = [[NSMutableArray alloc] init];

[array addObject:@""];
[array addObject:@(54)];Incompatible pointer types sending 'NSNumber *' to parameter of type 'NSString * __nonnull'
// Great, generics works as expected.
However I also have method I want to transform to generics
In header file:
- (NSArray <NSString*> *)objectsToSearch;
Implementation:
- (NSArray <NSString*> *)objectsToSearch
{
    NSString *first = @"1";

    NSString *second = @"2";

    NSString *third = @"3";

    NSNumber *test = @(55);

    return @[first, second, third, test]; // No-error!!!
}
Am I doing something wrong or Clang does not support generics + literals or there is something else I'm missing?
 解决方案 
I've just been diagnosing this some more and I don't think this is a bug. The following code shows a variety of options and why each will or will not compile. Note: This is based on my guesses as to how things work. It may be different to how Apple would explain it.
#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Wunused-variable"
-(void) testGenericArrays {

    NSString *aString = @"abc";
    NSNumber *aNumber = @(55);

    NSArray<NSString *> *arr1  = @[aString, aNumber];
    // Compiles because the RHS is an un-typed array at compilation time.

    NSArray<NSString *> *arr2  = @[aString, @(20)];
    // Compiles because the RHS is an un-typed array at compilation time.

    NSArray<NSString *> *arr3 = [NSArray<NSString *> arrayWithObjects:aString, aNumber, @(20), nil];
    // Compiles because the type erasure for arrayWithObjects only types the first argument which is a NSString.
    // The rest of the arguments are a vaList which is not checked during header processing.

    NSArray<NSString *> *arr4 = [NSArray<NSString *> arrayWithObjects:@(20), nil]; // <- Error!
    NSArray<NSString *> *arr5 = [NSArray<NSString *> arrayWithObjects:aNumber, nil]; // <- Error!
    // Neither of these two compile because the first argument is now a NSNumber and is checked.

    NSArray<NSString *> *arr6 = [NSArray<NSString *> arrayWithObject:aNumber]; // <- Error!
    // Doesn't compile because the argument is checked during header processing.

    NSArray<NSString *> *arr7 = [NSArray arrayWithObject:aNumber];
    // Compiles because the RHS is an un-typed array at compilation time.

    NSMutableArray<NSString *> *arr8 = [[NSMutableArray alloc] init];
    [arr8 addObject:aNumber]; // <- Error!
    // Doesn't compile because the LHS is a typed array and we are adding to it.
}
#pragma clang diagnostic pop
Hope this clarifies things for people. Feel free to cut and paste into a unit test and try it out for yourself.
                        
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