使用Null Coalescing运算符的独特方法

我知道在C#中使用Null合并运算符的标准方法是设置默认值.

string nobody = null;
string somebody = "Bob Saget";
string anybody = "";

anybody = nobody   ?? "Mr. T"; // returns Mr. T
anybody = somebody ?? "Mr. T"; // returns "Bob Saget"

但还有什么可以??用于？它不像三元运算符那样有用,除了比以下更简洁和更容易阅读:

nobody = null;
anybody = nobody == null ? "Bob Saget" : nobody; // returns Bob Saget

所以考虑到甚至更少知道空合并运算符......

你有没有用过??别的东西？

是??必要的,还是应该只使用三元运算符(大多数人都熟悉)

James Curran.. 208

嗯,首先,它比标准三元组更容易链接:

string anybody = parm1 ?? localDefault ?? globalDefault;

与

string anyboby = (parm1 != null) ? parm1 
               : ((localDefault != null) ? localDefault 
               : globalDefault);

如果null-possible对象不是变量,它也可以正常工作:

string anybody = Parameters["Name"] 
              ?? Settings["Name"] 
              ?? GlobalSetting["Name"];

与

string anybody = (Parameters["Name"] != null ? Parameters["Name"] 
                 : (Settings["Name"] != null) ? Settings["Name"]
                 :  GlobalSetting["Name"];

链接对于运营商来说是一个很大的优势,可以消除一堆冗余的IF (11认同)

Cristian Lib.. 173

我用它作为一个懒惰的负载单行:

public MyClass LazyProp
{
    get { return lazyField ?? (lazyField = new MyClass()); }
}

可读？自行决定.

嗯,首先,它比标准三元组更容易链接:

string anybody = parm1 ?? localDefault ?? globalDefault;

与

string anyboby = (parm1 != null) ? parm1 
               : ((localDefault != null) ? localDefault 
               : globalDefault);

如果null-possible对象不是变量,它也可以正常工作:

string anybody = Parameters["Name"] 
              ?? Settings["Name"] 
              ?? GlobalSetting["Name"];

与

string anybody = (Parameters["Name"] != null ? Parameters["Name"] 
                 : (Settings["Name"] != null) ? Settings["Name"]
                 :  GlobalSetting["Name"];

我用它作为一个懒惰的负载单行:

public MyClass LazyProp
{
    get { return lazyField ?? (lazyField = new MyClass()); }
}

可读？自行决定.

public int Compare(Person p1, Person p2)
{
    return PartialComparer.Compare(p1.Age, p2.Age)
        ?? PartialComparer.Compare(p1.Name, p2.Name)
        ?? PartialComparer.Compare(p1.Salary, p2.Salary)
        ?? 0;
}

string result = MyMethod() ?? "default value";

string result = (MyMethod () != null ? MyMethod () : "default value");

string methodResult = MyMethod ();
string result = (methodResult != null ? methodResult : "default value");

public class A
{
    var count = 0;
    private int? _prop = null;
    public int? Prop
    {
        get 
        {
            ++count;
            return _prop
        }
        set
        {
            _prop = value;
        }
    }
}

var a = new A();
var b = a.Prop == null ? 0 : a.Prop;

var b = a.Prop ?? 0

int? test = null;
var result = test ?? 0; // result is int, not int?

Dictionary PurchaseQuantities;
// PurchaseQuantities populated via ASP .NET MVC form.
var totalPurchased = PurchaseQuantities.Sum(kvp => kvp.Value ?? 0);
// totalPurchased is int, not int?

public string Error
{
    get
    {
        return this["Name"] ?? this["Address"] ?? this["Phone"];
    }
}

public string this[string columnName]
{
    get { ... }
}

public void Method(Arg arg = null)
{
    arg = arg ?? Arg.Default;
    ...

public class StackOverflow
{
    private IEnumerable _definitions;
    public IEnumerable Definitions
    {
        get
        {
            return _definitions ?? (
                _definitions = new List
                {
                    "definition 1",
                    "definition 2",
                    "definition 3"
                }
            );
        }
    } 
}