After reading Meanings of declaring, instantiating, initializing and assigning an object it talks about what initializing a variable means. But it doesn't explain what "initializing" an instance of a class means.

public class Test
{
   public static void Main()
   {
      Person person1 = new Person();
   }
}

public class Person
{
   // body
}

What does it mean to initialize an instance of a class?

CodePudding user response：

I prepared a blueprint for a car, but eventually I needed to send it to a factory to build it so I could actually use it

CodePudding user response：

Yeah, I don't like the "initialize" of the linked answer so much either, because it really only talks about giving a value to a single variable and doesn't really draw any distinctions between instantiation and assignment (the same lines of code are found in all of them) so for me it's a bit vague. We do have more specific processes (especially these days of modern c# syntax) when we talk about initialization

Initialize usually means "to give a created instance some initial values". Your class Person has nothing to initialize, so you could say that just by making it anew(instantiating) you've also done all the initialization possible and it's ready for use

Let's have something we can set values on

public class Person{
  public string Name {get;set;}
  public string Address {get;set;}

  public Person(string name){
    if(name == null) throw new ArgumentNullException(nameof(name));
    Name = name;
  }
}

Initializing as part of construction:

p = new Person("John");

Constructors force us to supply values and are used to ensure a developer gives a class the minimum set of data it needs to work.. a Person must have a name. Address is optional. We have created a person with the name initialized to John

Initializing post construction

You can give an instance additional (optional) values after you construct it, either like

p = new Person("Bill");
p.Address = "1 Microsoft Way";

Or

p = new Person("Bill"){
  Address = "1 Microsoft Way"
}

Which is a syntactic sugar the compiler unrolls to something like the first. We refer to everything in the { } brackets of the second example as "an object initializer". An important distinction here though is that the first form (p.Address=...) is not considered to be initialization by the compiler. If you made the address property like:

public string Address {get;init;}

Then it can only be set in a constructor or in an object initializer, which is the latter form above. The p.Address=... form would result in a compiler error if the property were declared with init

Props set just after construction are part of the initialization process (as an English/linguistic thing) though I wouldn't call it init if it was any further down the line, such as

p = new Person("Sam");

string addr = Console.ReadLine();

p.Address = addr; //not initialization

You might find cases where people talk about initialization in the sense for "the first time a variable or property is given a value" but that's also more a linguistic/English thing than a c# thing

The compiler knows how to perform other initialization, so we also call things like this "an initializer":

string[] x = new string[] {"a","b","c"};

The process of giving the array those 3 values is initialization, and the compiler will even take the type of the first argument and use it to make the array type, so an array can be type declared and ignited from the data:

var x = new[] {"a","b","c"};