问题描述
我发现自己现在在我的代码中经常使用当前模式
I find myself using the current pattern quite often in my code nowadays
var dictionary = new Dictionary<type, IList<othertype>>();
// Add stuff to dictionary
var somethingElse = dictionary.ContainsKey(key) ? dictionary[key] : new List<othertype>();
// Do work with the somethingelse variable
或者有时
var dictionary = new Dictionary<type, IList<othertype>>();
// Add stuff to dictionary
IList<othertype> somethingElse;
if(!dictionary.TryGetValue(key, out somethingElse) {
somethingElse = new List<othertype>();
}
这两种方式都感觉很迂回.我真正想要的是
Both of these ways feel quite roundabout. What I really would like is something like
dictionary.GetValueOrDefault(key)
现在,我可以为字典类编写一个扩展方法来为我做这件事,但我想我可能会遗漏一些已经存在的东西.SO,有没有一种方法可以在不为字典编写扩展方法的情况下以更容易看"的方式做到这一点?
Now, I could write an extension method for the dictionary class that does this for me, but I figured that I might be missing something that already exists. SO, is there a way to do this in a way that is more "easy on the eyes" without writing an extension method to dictionary?
推荐答案
TryGetValue
已经将类型的默认值分配给字典,因此您可以使用:
TryGetValue
will already assign the default value for the type to the dictionary, so you can just use:
dictionary.TryGetValue(key, out value);
并忽略返回值.然而,那真的将只返回default(TValue)
,而不是一些自定义的默认值(也不是,更有用的是,执行委托的结果).框架中没有任何更强大的内置功能.我建议两种扩展方法:
and just ignore the return value. However, that really will just return default(TValue)
, not some custom default value (nor, more usefully, the result of executing a delegate). There's nothing more powerful built into the framework. I would suggest two extension methods:
public static TValue GetValueOrDefault<TKey, TValue>
(this IDictionary<TKey, TValue> dictionary,
TKey key,
TValue defaultValue)
{
TValue value;
return dictionary.TryGetValue(key, out value) ? value : defaultValue;
}
public static TValue GetValueOrDefault<TKey, TValue>
(this IDictionary<TKey, TValue> dictionary,
TKey key,
Func<TValue> defaultValueProvider)
{
TValue value;
return dictionary.TryGetValue(key, out value) ? value
: defaultValueProvider();
}
(当然,您可能想要进行参数检查:)
(You may want to put argument checking in, of course :)
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