“如果对象为空则为空，或者如果对象不为空则为 object.member"的快捷方式 [英] Shortcut for "null if object is null, or object.member if object is not null"

问题描述

我正在尝试编写一个通用的扩展方法，让我这样做:

I'm trying to write a generic extension method that let's me do this:

this.startDate = startDateXAttribute.NullOrPropertyOf<DateTime>(() =>
{
    return DateTime.Parse(startDateXAttribute.Value);
});

NullOrPropertyOf() 将返回 null 如果它用于 null 对象(例如，如果 startDateXAttribute 是 null)，或者返回一个 Func 的结果，如果它不为 null.

NullOrPropertyOf() would return null if it's used on a null object (e.g. if startDateXAttribute was null), or return the result of a Func if it's not null.

这个扩展方法会是什么样子?

What would this extension method look like?

推荐答案

没有简短的形式；实现一个是一个相当频繁要求的功能.语法可能类似于:

There's no short form for that; implementing one is a fairly frequently requested feature. The syntax could be something like:

x = foo.?bar.?baz;

也就是说，如果 foo 或 foo.bar 为 null，则 x 为 null，如果它们都不为 null，则为 foo.bar.baz 的结果.

That is, x is null if foo or foo.bar are null, and the result of foo.bar.baz if none of them are null.

我们在 C# 4 中考虑过它，但它并没有使它靠近优先级列表的顶部.对于该语言的假设未来版本，我们会牢记这一点.

We considered it for C# 4 but it did not make it anywhere near the top of the priority list. We'll keep it in mind for hypothetical future versions of the language.

更新:C# 6 将具有此功能.有关设计注意事项的讨论，请参阅 http://roslyn.codeplex.com/discussions/540883.

UPDATE: C# 6 will have this feature. See http://roslyn.codeplex.com/discussions/540883 for a discussion of the design considerations.

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