[英]C# What is this initialization doing if it doesn't have the 'new'?
我錯過了它甚至編譯的內容/方式,以及它試圖做什么:
// throws null reference exception on 'get' for C1:
var c2 = new Class2 { C1 = { Value = "stg" } };
public class Class1
{
public string Value { get; set; }
}
class Class2
{
public Class1 C1 { get; set; }
}
很明顯,初始化應該包括“新”:
var c2 = new Class2 { C1 = new Class1 { Value = "stg" } };
但是即使沒有“新”,這又是如何編譯的,它試圖做什么?
建造
var c2 = new Class2 { C1 = { Value = "stg" } };
是一種語法糖,展開成
Class c2 = new Class2();
c2.C1.Value = "stg"; // <- Here we have the exception thrown
對於編譯器來說, C1
是null
並不明顯( C1
可以在構造函數中創建),這就是代碼編譯的原因。
編輯:為什么編譯器允許C1 = { Value = "stg" }
? 這很方便(語法糖是為了我們的方便),想象一下:
public class Class1 {
public string Value { get; set; }
}
class Class2 {
// Suppose, that in 99% cases we want C1 with Value == "abc"
// But only when Class1 instance is a property C1 of Class2
public Class1 C1 { get; set; } = new Class1() { Value = "abc" };
}
...
// however, in our particular case we should use "stg":
var c2 = new Class2 { C1 = { Value = "stg" } };
// for some reason I recreate C1 (note "new"):
var otherC2 = new Class2 { C1 = new Class1 { Value = "stg" } };
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