C# | Syntax to Initialize New Object With Properties of Another Instance

Question

C# Initialize Object With Properties of Another Instance

(A) I can do this...

var newRestaurant = new Restaurant();
newRestaurant.Cuisine = model.Cuisine;
newRestaurant.Name = model.Name;

(B) And I can write it this way...

var newRestaurant = new Restaurant() { Name = model.Name };

(C) But how come I can't write it like so...

var newRestaurant = new Restaurant() model;

(Q) Isn't (B) just an Object-Literal while (C) is an object instance?

Would love to know.

Thx

You'll have to ask MS why they haven't added this feature yet. We can't possibly answer why they haven't chosen to add any particular feature to the language. — Servy, Dec 09 '16 at 18:14
why not create a method with `System.Reflection` to populate a object with the values of another, and put this in a constructor that receive a object of the same type as param? — Lucas, Dec 09 '16 at 18:14
(B) is an object initializer and is just syntactic sugar for `var newRestaurant = new Restaurant(); newRestaurant.Name = model.Name;` — itsme86, Dec 09 '16 at 18:14
@itsme86 Almost, there's actually a temp variable involved as the assignment to `Name` will occur before the assignment to `newRestaurant`. — juharr, Dec 09 '16 at 18:17
Got it, thx guys. I'm a bit of a greenhorns (obviously) with C# -- this helps a lot. — Cody, Dec 09 '16 at 18:22

Alex Van Liew · Accepted Answer · 2016-12-09T18:28:19.697

Isn't (B) just an Object-Literal while (C) is an object instance?

The short answer? No. C# doesn't use curly braces to represent object literals like JavaScript or similar languages do; C# uses curly braces to refer to blocks.

In the code

var newRestaurant = new Restaurant() { Name = model.Name };

the { Name = model.Name } part isn't an object literal, it's an initializer block. You can use a similar syntax to initialize collections like lists and dictionaries:

var myString = "string3";
var myList = new List<string>() { "string1", "string2", myString };
var myDictionary = new Dictionary<string, int>() 
{
    { "string1", 1 },
    { "string2", 2 },
    { myString, 3 },
};

As you can see, the syntax of these blocks differs based on what sort of object is before them. This code is transformed by the compiler into

var myString = "string3";
var myList = new List<string>();
myList.Add("string1");
myList.Add("string2");
myList.Add(myString);
var myDictionary = new Dictionary<string, int>();
myDictionary.Add("string1", 1);
myDictionary.Add("string2", 2);
myDictionary.Add(myString, 3);

And in the case of your example, it's transformed into:

var newRestaurant = new Restaurant(); 
newRestaurant.Name = model.Name;

When you try and use model like var newRestaurant = new Restaurant() model;, the compiler has no idea what sorts of properties are in model or what you meant to do with them; are you trying to add to a list? Are you trying to copy all the properties? What does it do if all the properties in model don't match?

C# | Syntax to Initialize New Object With Properties of Another Instance

C# Initialize Object With Properties of Another Instance

1 Answers1

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