C#-“是"后的花括号的含义操作员 [英] C# - meaning of curly braces after the "is" operator

问题描述

我在某些C#源代码中找到以下行:

I found in some C# source code the following line:

if(！(context.Compilation.GetTypeByMetadataName("Xunit.FactAttribute")是{} factAttribute))

这是另一个:

if(！(diagnostic.Location.SourceTree是{}树))

is 运算符后的花括号( {} )是什么意思?

What is the meaning of the curly braces ({ }) after the is operator?

推荐答案

这是C#8.0中引入的新模式匹配功能，称为

This is a new pattern matching feature which was introduced in C# 8.0 and is called property pattern. In this particular case it is used to check that object is not null, example from linked article:

static string Display(object o) => o switch
{
    Point { X: 0, Y: 0 }         p => "origin",
    Point { X: var x, Y: var y } p => $"({x}, {y})",
    {}                           => o.ToString(),
    null                         => "null"
};

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