如何使用 Obj-C 块实现 whileTrue 控制流方法？

发布于 2024-12-03 05:49:32 字数 384 浏览 0 评论 0原文

是否可以使用块在 Objective-C 中实现类似 Smalltalk 风格的 whileTrue: 方法？具体来说，而不是：

int count = 0;
while (count < 10)
{
  NSLog(count);
  count++;
}

我希望能够（通过称为 OOBoolean 的 bool 原语上的包装器）执行类似...

__block int count = 0;
[[OOBoolean booleanWithBool: count < 10] whileTrueDo: ^() {
  NSLog(count);
  count++;
}];

我无法理解这是如何实现的...

原文

Is it possible to implement something like a Smalltalk-style whileTrue: method in Objective-C using blocks? Specifically, instead of:

int count = 0;
while (count < 10)
{
  NSLog(count);
  count++;
}

I'd like to be able to do (via a wrapper on the bool primitive called OOBoolean) something like...

__block int count = 0;
[[OOBoolean booleanWithBool: count < 10] whileTrueDo: ^() {
  NSLog(count);
  count++;
}];

I'm having trouble understanding how this would be implemented though...

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我要还你自由 2024-12-10 05:49:32

这里你有几个想法，

假设你的 bool 包装器实现 boolValue，一个简单的实现可能是：

-(void) whileTrueDo:(void (^)(void)) block{
    while ([self boolValue]) {
        block();
    }
}

为了让包装器在每次迭代后更改其 bool 值，该块必须能够实际更改用于计算的变量布尔条件。因此，在您的情况下，通过将 __block 类型修饰符设置为 count，并增加每个块执行中的计数，您应该能够使其工作。

问题是，如果您通过发送评估条件来创建包装器，正如您在问题中所述，您将无法在每次迭代中更改其 bool 值。因此，我将更改包装器的创建方式和 whileTrueDo: naive 实现，以便布尔包装器使用评估块。

   __block int count = 0;
    OOBooleanBlock evaluationBlock =  ^BOOL{
        return count < 10;
    };
    [[OOBoolean booleanWithBlock:evaluationBlock] whileTrueDo: ^() {
        NSLog(count);
        count++;
    }];

//In OOBoolean 
+(OOBoolean*) booleanWithBlock:(OOBooleanBlock) evaluationBlock{
//Instantiate, set the evaluationBlock ivar and return the ooboolean object.
} 

-(void) whileTrueDo:(void (^)(void)) block{
    while (self.evaluationBlock()) {
        block();
    }
}

记得使用__block类型修饰符，否则会进入无限循环。

我还没有测试过这个，但我希望这对你有帮助。

干杯

Here you have a couple of ideas,

Assuming your bool wrapper implements boolValue, a naive implementation could be:

-(void) whileTrueDo:(void (^)(void)) block{
    while ([self boolValue]) {
        block();
    }
}

In order for the wrapper to change its bool value after each iteration, the block must be able to actually change the variable that is used to calculate the boolean condition. So, in your case, by setting the __block type modifier to count, and increasing count in each block execution, you should be able to make it work.

The problem is, if you create your wrapper by sending the evaluated condition, as you stated in your question, you wont be able to change its bool value in each iteration. So, I would change the way the wrapper is created and the whileTrueDo: naive implementation so the boolean wrapper uses an evaluation block.

   __block int count = 0;
    OOBooleanBlock evaluationBlock =  ^BOOL{
        return count < 10;
    };
    [[OOBoolean booleanWithBlock:evaluationBlock] whileTrueDo: ^() {
        NSLog(count);
        count++;
    }];

//In OOBoolean 
+(OOBoolean*) booleanWithBlock:(OOBooleanBlock) evaluationBlock{
//Instantiate, set the evaluationBlock ivar and return the ooboolean object.
} 

-(void) whileTrueDo:(void (^)(void)) block{
    while (self.evaluationBlock()) {
        block();
    }
}

Remember to use the __block type modifier, otherwise you will enter in an infinite loop.

I haven't tested this, I hope this helps you though.

Cheers

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