调用链中的空合并 [英] Null coalescing within an invocation chain

问题描述

如果我有对象的一个​​长长的清单，每有一个LINQ的，其中内返回null条款，如可能性

If I have a long list of objects that each has the possibility of returning null within a "Linq where" clause, e.g.

 SomeSource.Where(srcItem=>(srcItem.DataMembers["SomeText"].Connection.ConnectedTo as Type1).Handler.ForceInvocation == true));

索引可以返回空值和为运营商可能返回null。这是可能的对象没有连接（即该属性为null）。
。如果一个空的任何地方遇到过，我想在where子句返回假，对于项目进行评估。相反，它有一个空引用异常中止。

the indexer can return null and the "as" operator may return null. It is possible that the object does not have a connection (ie. The property is null). If a null is encountered anywhere, I would like the where clause to return "false" for the item being evaluated. Instead, it aborts with a null reference exception.

在我看来，这将是做作到一个C＃表达式中表达出来。我不喜欢创建一个多行语句或为其创建一个单独的FUNC。
有一些使用我失踪的空合并运算符的？

It appears to me that this would be contrived to express within a single C# expression. I don't like to create a multi line statement or create a separate func for it. Is there some use of the null coalescing operator that I'm missing?

推荐答案

您正在寻找的？运营商（或者是它？那些酮，反正），这并不在C＃中存在（虽然它是一个经常被请求的功能，根据埃里克利珀）。

You're looking for the .? operator (or is it ?.—one of those, anyway), which does not exist in C# (though it is an often-requested feature, according to Eric Lippert).

唯一的可能的建议，我已经是编写需要一个表达式的方法和用途的是的检查任何空值。但是，这会在性​​能成本。无论如何，它可能看起来像：

The only possible suggestion I have is to write a method that takes an expression and uses it to check for any nulls. But this will come at a performance cost. Anyway, it might look like:

T TryOrDefault<T>(Expression<Func<T>> expression)
{
    // Check every MemberExpression within expression one by one,
    // looking for any nulls along the way.

    // If a null is found, return default(T) or some default value.

    // Otherwise...
    Func<T> func = expression.Compile();
    return func();
}

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