问题
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a curious c# syntax
So I've seen some code around and a few of them use a ? after the type, like this:
private Point? loc = null;
So I'm wondering if Point? is different than Point (can't put a question mark at the end of my sentence or I'll confuse you guys ... :] ). The language I'm using is C# by the way.
回答1:
T? is a shorthand (in C#) for Nullable<T> - so Point? is another way of writing Nullable<Point> or example.
See sections 1.3 and 4.1 of the C# 3 language spec - and various other places, to be honest - for more details. See the docs for System.Nullable<T> for more information from the framework side of things. Or read chapter 4 of C# in Depth :) (Unfortunately it's not one of the free chapters.)
(This question is bound to be a duplicate, but I don't have the energy to find it right now.)
回答2:
Point? is the same as Nullable<Point>. It allows you to assign null to value types, such as structs.
回答3:
It means the type can accept its' value and null.
来源：https://stackoverflow.com/questions/2079334/what-does-the-mean-after-a-type