在 C# 中创建 object 的实例时，带和不带 () 符号有什么区别？

Question

I have a class

public class Product
{
    public string Name { get; set; }
}

Could you please help me to explain the difference between two case of creating the instance of class below?

var instanceOne = new Product
{
    Name = "iPhone 4"
}

and

var instanceTwo = new Product()
{
    Name = "iPhone 5"
}

Thanks

Answer 1

There is no difference, they're the same (assuming you meant to initialize the Name property, not define it, and it can't be static), except for one very specific case:

Product instanceOne = new()
{
    Name = "arf"
};

If you use type-targetted new , you have to use the new() {...} version, because new {...} defines an anonymous type instead.

Answer 2

The () is redundant in the following example:

var instanceTwo = new Product()
{
    Name = "iPhone 5"
}

You can just write:

var instanceTwo = new Product // <----- () deleted
{
    Name = "iPhone 5"
}

Answer 3

There is no difference between these two.

Please note that object initalisers allow specifying constructor parameters too.

class Cat 
{
    public Cat() {}

    public Cat(string name) { Name = name; }

    public string Name { get; set; }

    public string Color { get; set; }
}

(...)

var lightning = new Cat(Name: "Lightning")
{
    Color = "White"
};

var storm = new Cat
{
    Name = "Storm",
    Color = "Gray"
};

A tiny bit more

Please also note that

var storm = new Cat
{
    Name = "Storm",
    Color = "Gray"
};

is not the same as

var storm = new Cat();
storm.Name = "Storm";
storm.Color = "Gray";

The former results in:

var __a = new Cat();
__a.Name = "Storm";
__a.Color = "Gray"; 
var storm = __a;

as shown in Overview of C# 3.0 .