有没有如果使用一个对象初始化，或者是asthetic的性能改进？ [英] Is there a performance improvement if using an object initializer, or is it asthetic?

问题描述

因此，比较会之间：

MyClass foo = new MyClass();
foo.Property1 = 4;
foo.Property2 = "garfield";

和

MyClass foo = new MyClass { Property1 = 4, Property2 = "garfield" };

它是语法糖，或者是有实际一些性能增益（不过分钟，它很可能是？）

Is it syntactic sugar, or is there actually some kind of performance gain (however minute it's likely to be?)

推荐答案

它实际上有可能的非常的稍慢使用对象初始化，而不是调用一个构造函数，然后分配的属性，因为它有一个额外的任务：

It's actually potentially very, very slightly slower to use an object initializer than to call a constructor and then assign the properties, as it has one extra assignment:

MyClass foo = new MyClass();
foo.Property1 = 4;
foo.Property2 = "garfield";

VS

vs

MyClass tmp = new MyClass();
tmp.Property1 = 4;
tmp.Property2 = "garfield";
MyClass foo = tmp;

之前参考被分配给变量的属性都被分配。这种差异是一个的可见的之一，如果它的重用一个变量：

The properties are all assigned before the reference is assigned to the variable. This difference is a visible one if it's reusing a variable:

using System;

public class Test
{
    static Test shared;

    string First { get; set; }

    string Second
    {
        set
        {
            Console.WriteLine("Setting second. shared.First={0}",
                              shared == null ? "n/a" : shared.First);
        }
    }

    static void Main()
    {
        shared = new Test { First = "First 1", Second = "Second 1" };
        shared = new Test { First = "First 2", Second = "Second 2" };        
    }
}

输出显示，在第二行主要，当二正在设置（后首先）中， shared.First 的值仍然是第一 - 即共享尚未分配的新的价值呢。

The output shows that in the second line of Main, when Second is being set (after First), the value of shared.First is still "First 1" - i.e. shared hasn't been assigned the new value yet.

正如马克说，虽然，你几乎可以肯定从来没有真正发现一个差异。

As Marc says though, you'll almost certainly never actually spot a difference.

匿名类型有保证使用构造函数 - 的形式在C＃3语言规范的第7.5.10.6给出

Anonymous types are guaranteed to use a constructor - the form is given in section 7.5.10.6 of the C# 3 language specification.

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