objective-c NSString：isEqual 与 isEqualToString

NSString: isEqual vs. isEqualToString

提问by Jaka Jan?ar

What is the difference between isEqual:and isEqualToString:?

isEqual:和 和有isEqualToString:什么区别？

Why are classes adding isEqualTo* methods (isEqualToArray for NSArray, isEqualToData for NSData, ...) instead of just overriding isEqual:?

为什么类要添加 isEqualTo* 方法（NSArray 的 isEqualToArray，NSData 的 isEqualToData，...）而不是仅仅覆盖isEqual:？

回答by Abizern

isEqual:compares a string to an object, and will return NOif the object is not a string. isEqualToString:is faster if you know both objects are strings, as the documentationstates:

isEqual:将字符串与对象进行比较，NO如果对象不是字符串则返回。isEqualToString:如果您知道两个对象都是字符串，速度会更快，如文档所述：

Special Considerations

When you know both objects are strings, this method is a faster way to check equality than isEqual:.

特别注意事项

当您知道两个对象都是字符串时，此方法是检查相等性的一种比 更快的方法isEqual:。

isEqualTo<Class>is used to provide specific checks for equality. For instance; isEqualToArray:checks that the arrays contain an equal number of objects, and that the objects at a given index return YESfor the isEqual:test.

isEqualTo<Class>用于提供特定的相等性检查。例如; isEqualToArray:检查数组是否包含相同数量的对象，并且给定索引处的对象返回YES用于isEqual:测试。

回答by Jonathan Dann

Also, for writing your own -isEqual:and -isEqualTo<Class>:methods, the convention is to allow nil arguments for -isEqual:and raise an exception for nil arguments to -isEqualTo<Class>:

另外，编写自己-isEqual:和-isEqualTo<Class>:方法，惯例是允许零论点-isEqual:，提高了无参数异常-isEqualTo<Class>:

回答by respectTheCode

Expanding on @Abizern and @Jonathan Dann answers, both isEqualand isEqualToStringwork with nilvalues.

扩展@Abitern 和@Jonathan Dann 的答案，isEqual并isEqualToString与nil价值观一起工作。

- (void)testStringEqual {
    NSString *string = nil;

    STAssertFalse([string isEqual:@"test"], @"NSString isEqual");
    STAssertFalse([string isEqualToString:@"test"], @"NSString isEqualToString");

    // Note that these both return NO
    STAssertFalse([string isEqual:nil], @"NSString isEqual");
    STAssertFalse([string isEqualToString:nil], @"NSString isEqualToString");

    string = @"test";

    STAssertTrue([string isEqual:@"test"], @"NSString isEqual");
    STAssertTrue([string isEqualToString:@"test"], @"NSString isEqualToString");

    STAssertFalse([string isEqual:nil], @"NSString isEqual");
    STAssertFalse([string isEqualToString:nil], @"NSString isEqualToString");
}

回答by iKenndac

My guessis that it provides a slight performance enhancement, as isEqualToString: won't have to type-check what's passed in.

我的猜测是它提供了轻微的性能增强，因为 isEqualToString: 不必对传入的内容进行类型检查。

回答by Ben Packard

I highly recommend this. The performance benefits of isEqualToString are basically negligible for most applications. But there are two other distinctions the author mentions:

我强烈推荐这个。isEqualToString 的性能优势对于大多数应用程序来说基本上可以忽略不计。但作者还提到了另外两个区别：

• Type safety
• The way nilis handled

• 类型安全
• 的方式nil被处理