Meanings of declaring, instantiating, initializing and assigning an object

Question

Technically what are the meanings and differences of the terms declaring, instantiating, initializing and assigning an object in C#?

I think I know the meaning of assigning but I have no formal definition.

In msdn, it is said "the act of creating an object is called instantiation". But the meaning creating seems vague to me. You can write

int a;

is a then created?

i have never seen `clarifying`. but `instantiating` means to create an instance of an object. `initializing` means setting value to an object.(does not necessarily create new instance). `assigning` is self descriptive. assign a value to an object. i maybe wrong. but thats what i think — M.kazem Akhgary, Aug 29 '15 at 21:42
declaring is just what you have shown. like `int a;` you declared an `int` named `a` but you still not initialized it. — M.kazem Akhgary, Aug 29 '15 at 21:52
@M.kazemAkhgary after this declaration, does `a=2` initialize it? instantiate it? — Minimus Heximus, Aug 29 '15 at 21:55
instantiate is for class objects. means create a new object with new reference. for a=2 you say initialize. — M.kazem Akhgary, Aug 29 '15 at 21:57
@OldProgrammer Do you mean `a` is not an object because `int` is not a class? — Minimus Heximus, Aug 29 '15 at 22:32
Related: https://stackoverflow.com/questions/2330767/what-is-the-difference-between-instantiated-and-initialized — nawfal, Jul 03 '16 at 21:20

score 61 · Accepted Answer · answered Aug 29 '15 at 21:55

61

Declaring - Declaring a variable means to introduce a new variable to the program. You define its type and its name.

int a; //a is declared

Instantiate - Instantiating a class means to create a new instance of the class. Source.

MyObject x = new MyObject(); //we are making a new instance of the class MyObject

Initialize - To initialize a variable means to assign it an initial value.

int a; //a is declared
int a = 0; //a is declared AND initialized to 0
MyObject x = new MyObject(); //x is declared and initialized with an instance of MyObject

Assigning - Assigning to a variable means to provide the variable with a value.

int a = 0; //we are assigning to a; yes, initializing a variable means you assign it a value, so they do overlap!
a = 1; //we are assigning to a

answered Aug 29 '15 at 21:55

Zarwan

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So Instantiation is not used for structs or simple types? – Minimus Heximus Aug 29 '15 at 22:00
Can "initializing" mean "assigning for the first time after declaration"? – Minimus Heximus Aug 29 '15 at 22:04
1

The term is used for structs, although I am honestly not sure why. However "instantiate" is not used for simple types. And yes, that is basically the meaning of initialize. @MinimusHeximus – Zarwan Aug 29 '15 at 22:10

Dave Cousineau · Answer 2 · 2015-08-29T22:32:58.157

In general:

Declare means to tell the compiler that something exists, so that space may be allocated for it. This is separate from defining or initializing something in that it does not necessarily say what "value" the thing has, only that it exists. In C/C++ there is a strong distinction between declaring and defining. In C# there is much less of a distinction, though the terms can still be used similarly.

Instantiate literally means "to create an instance of". In programming, this generally means to create an instance of an object (generally on "the heap"). This is done via the new keyword in most languages. ie: new object();. Most of the time you will also save a reference to the object. ie: object myObject = new object();.

Initialize means to give an initial value to. In some languages, if you don't initialize a variable it will have arbitrary (dirty/garbage) data in it. In C# it is actually a compile-time error to read from an uninitialized variable.

Assigning is simply the storing of one value to a variable. x = 5 assigns the value 5 to the variable x. In some languages, assignment cannot be combined with declaration, but in C# it can be: int x = 5;.

Note that the statement object myObject = new object(); combines all four of these.

new object() instantiates a new object object, returning a reference to it.
object myObject declares a new object reference.
= initializes the reference variable by assigning the value of the reference to it.

@MinimusHeximus Define means give a value (or body) to. We don't really use "define" much in C#, but it would be similar in meaning to initialize. When you write a method, I guess you could call that defining the method, though it doesn't have any contrast with declaring the method like it would in C++. — Dave Cousineau, Aug 29 '15 at 22:35

Meanings of declaring, instantiating, initializing and assigning an object

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