字典直接访问与TryGetValue [英] Dictionary Direct access vs TryGetValue

问题描述

我有一个字典，它将字符串映射到这样的对象: Dictionary<string, object> myDic;

I have a dictionary which maps strings to objects like this: Dictionary<string, object> myDic;

我事先知道对象的类型是基于字符串的，但是我的问题是我应该使用TryGetValue还是使用try，catch语句直接查找.

I know prior what the type of the object is based on the string, but my question is whether I should use TryGetValue, or direct lookups with try, catch statements.

示例:

//TryGetValueMethod
object myObject = null;
myDic.TryGetValue("test", out myObject);

MyCustomType t1 = (MyCustomType) myObject;

//Direct lookup method
try
{
     MyCustomType t2 = (MyCustomType) myDic["test"];
     //Do something here...
} catch {}

您认为首选哪种方法?第二个是更干净的编码，因为没有多余的强制转换，但是我认为它的效率比第一个低，因为它没有异常.

What method do you think is preferred? The second one is more clean coding because there are no extra castings, but i think it is less efficient than the first, because it is exception-free.

推荐答案

我不认为您应该使用try/catch来形成这样的逻辑路径. Exception应该是例外情况，其中某些地方出了错".

I don't think you should use try/catch to form a logical path like that. Exceptions are supposed to be exceptional cases, where something has "gone wrong".

我个人更喜欢ContainsKey:

if (myDic.ContainsKey("test")) {
   MyCustomType value = myDic["test"];
   // do something with the value
}

如果您认为未找到密钥意味着某事出错"，那么我将省略测试，并在找不到密钥的情况下抛出异常.

If you think that not finding the key means that something has "gone wrong", then I would omit the test, and let an exception be thrown if the key is not found.

这些天来，我尝试改用TryGetValue.有点笨拙，但是一旦您习惯了它，还算不错.

these days I try to use TryGetValue instead. It's slightly more clumsy, but once you get used to it, it's not so bad.

MyCustomType value;
if (myDic.TryGetValue("test", out value)) {
   // do something with value
}

现在，在out var中，我肯定会更多地使用TryGetValue.类似地，您可以编写一个CantGetValue方法(具有相反的布尔结果的方法)，因为在大多数情况下，您想要在没有的情况下(而不是在没有值的情况下)做一些额外的事情. /p>

Now with out var I definitely use TryGetValue a lot more. Similarly you can write a CantGetValue method (same thing with opposite boolean result), since most of the time you want to do something extra when there isn't a value, not when there is.

if (dict.TryGetValue("test", out var value)) {
   // do something with value
}

// or

if (cache.CantGetValue("test", out var cachedValue)) {
   // cache value
}
// make use of value

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