在Objective-C中，方法的绑定是否真的发生在“运行时”？ [英] In Objective-C, does the binding of method really happen at "run-time"?

问题描述

我听说Objective-C受到SmallTalk消息传递机制的影响。

Objective-C，像Smalltalk一样，可以使用动态输入：一个对象可以是
发送一条未在其界面。这可以允许
增加灵活性，因为它允许对象捕获一个
消息，并将消息发送到可以适当响应
的另一个对象，或者同样发送消息到另一个
对象。

我感觉到像 [anObject someMethod] / code>，绑定 someMethod 到机器代码可能会在运行时发生。

因此，我写了一个这样的演示：

  #import< Foundation / Foundation.h> 
 
 @interface Person：NSObject {
 @private char * name; 
} 
 @property（readwrite，assign）char * name; 
  - （void）sayHello; 
 @end 
 
 @implementation Person 
 @synthesize name; 
 
  - （void）sayHello {
 printf（你好，我的名字是％s！\\\
，[self name]）; 
} 
 
 
 @end 
 
 int main（）{
 Person * brad = [Person new]; 
 brad.name =Brad Cox; 
 [brad sayHello]; 
 [brad sayHelloTest]; 
 
 
} 
  

我尝试过 [brad sayHelloTest] 发送 brad 一条消息 sayHelloTest 哪个 brad 不知道如何处理..我预计在编译时不会发生错误..

然而，编译器仍然抛出错误：

  main.m：24：11：error：实例方法'-sayHelloTest'未找到（返回类型默认为'id'）[-Werror，-Wobjc-method-access] 
 [brad sayHelloTest]; 
 ^ ~~~~~~~~~~~ 
 main.m：3：12：note：receiver是这里声明的类的实例
 @interface Person：NSObject {
 ^ 
  

更改 [（id）brad sayHelloTest] 到 [（id）brad sayHelloTest]; 不工作..（编译命令是 clang -Wall -Werror -g - v main.m -lobjc -framework Foundation -o main ）

在Objective-C中，方法的绑定是否真的发生在run -时间？如果是这样，为什么会有这样的编译器错误？

如果绑定没有发生在运行时，为什么Objective-C被称为动态打字语言？

有没有人对此有任何想法？

解决方案

/ p>

在编译过程中抛出错误，因为包含 -Werror 标志，这将会变为警告进入错误 ..

http://clang.llvm.org/docs/UsersManual.html#cmdoption-Werror

删除 -Werror 标志，一切正常工作，错误只在运行时发生。

I heard that Objective-C is influenced by the "message passing mechanism" of SmallTalk.

Objective-C, like Smalltalk, can use dynamic typing: an object can be sent a message that is not specified in its interface. This can allow for increased flexibility, as it allows an object to "capture" a message and send the message to a different object that can respond to the message appropriately, or likewise send the message on to another object.

And I felt for codes like [anObject someMethod], the binding of someMethod to the machine code may happen at run-time..

Therefore, I write a demo like this:

#import <Foundation/Foundation.h>

@interface Person : NSObject {
    @private char *name;
}
@property (readwrite, assign) char *name;
- (void)sayHello;
@end

@implementation Person
@synthesize name;

- (void)sayHello {
    printf("Hello, my name is %s!\n", [self name]);
}


@end

int main() {
    Person *brad = [Person new];
    brad.name = "Brad Cox";
    [brad sayHello];
    [brad sayHelloTest];


}

I tried [brad sayHelloTest] to send brad a message sayHelloTest which brad doesn't know how to handle with.. I expect the error will NOT happen at compile-time..

However, the compiler still throws an error:

main.m:24:11: error: instance method '-sayHelloTest' not found (return type defaults to 'id') [-Werror,-Wobjc-method-access]
    [brad sayHelloTest];
          ^~~~~~~~~~~~
main.m:3:12: note: receiver is instance of class declared here
@interface Person : NSObject {
           ^

Change [(id)brad sayHelloTest] to [(id)brad sayHelloTest]; doesn't work either.. (The compiling command is clang -Wall -Werror -g -v main.m -lobjc -framework Foundation -o main)

In Objective-C, does the binding of method really happen at "run-time"? If so, why will there be a compiler error like this?

If the binding doesn't happen at "run-time", why was "Objective-C" called "dynamic typing language"?

Does anyone have any ideas about this?

解决方案

I figured out the reason finally..

It throw errors during compiling because -Werror flag is included, which will turn warning into error..

http://clang.llvm.org/docs/UsersManual.html#cmdoption-Werror

After I delete -Werror flag, everything works as expected and the error only happens at run-time.

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