C#•15mo ago

❔ why new is needed for reference types

Can someone explain why the new operator is used for references types but not value types. When I assign an variable x of type int to 10 is 10 just binary in the computer or an object of the int class. And what does it mean for to store references to your data and how is that the same as an object

64 Replies

Pobiega•15mo ago

Because value typed have an implicit default value Reference types don't, they default to null

FigureOP•15mo ago

But don't reference types just hold values, like in a array couldn't you look at the values inside and see the type

Angius•15mo ago

Also, structs are value types and also need to be newed up

Pobiega•15mo ago

Oh, you are talking specifically about literal values

FigureOP•15mo ago

Yeah What is a struct

Angius•15mo ago

I'd go more along the lines of "primitives don't need to be newed up" While complex types that consist of those primitives, do It's like a class but lives on the... uh... stack? Can never remember what lives in the stack and what on the heap lol

FigureOP•15mo ago

So literal values are structs

Pobiega•15mo ago

Class on heap

Angius•15mo ago

And struct on stack, so I was correct, nice Technically not all of them, since System.String is a class due to struct's size limitations

FigureOP•15mo ago

Pobiega•15mo ago

When you do int x = 10; a place in the stack (assuming this is a local variable) will be reserved to hold an integer, currently with the value 10 you can later do x = 123456; and the value stored there changes, but the size and location of the reservation in the stack remains the same

FigureOP•15mo ago

Pobiega•15mo ago

new is how we call the constructor for a class/struct, and thats what that keyword does int doesnt need a constructor, as its values are always stored directly

FigureOP•15mo ago

So is array a class or does each data type have an array

Pobiega•15mo ago

array is something else. its a reference type thou. but its not a class int[] is not the same as Array

FigureOP•15mo ago

I thought int[] ,was an reference type

Pobiega•15mo ago

it is its an array. something can be a reference type without being a class

FigureOP•15mo ago

But it's also a class? Ok

Pobiega•15mo ago

I literally just said twice that its not a class

FigureOP•15mo ago

I thought you meant array not int[]

Pobiega•15mo ago

int[] IS an array. its just not an Array

FigureOP•15mo ago

Ok. And int[] is. Struct

Pobiega•15mo ago

no its an array. its its own thing

FigureOP•15mo ago

I thought you said new makes classes and structs

Pobiega•15mo ago

int[] is a reference to a piece of memory new int[5] is the space required for 5 ints, consecutively all initialized to 0, by default

arion•15mo ago

For note here, the static class Array is not [] Though the [] is a reference type which its content's point to something in memory

Pobiega•15mo ago

thats what I've been trying to say 🙂

FigureOP•15mo ago

And the constructor makes the space for those 5 ints

Pobiega•15mo ago

yeah. it couldnt do that before, as it didnt know what size of array you wanted

FigureOP•15mo ago

so basically arrays hold variables

Pobiega•15mo ago

int[] is the type of the variable, much like string or List<String> etc an array with length 5 and one with length 10000 have the same type, int[] I wouldn't say that, its one variable holding Length amount of items

int[] xs = new int[10];
xs[7] = 555;

int[] xs = new int[10];
xs[7] = 555;

this is valid, and just sets the value of the 8th integer to 555

FigureOP•15mo ago

Ok thank you for the help

Pobiega•15mo ago

333fred•15mo ago

More correctly, structs live where their containers live. A struct field of a class is on the heap, because that's where its container is Arrays are classes, but they're very special. Both C# and the runtime have special instructions just for them It's perfectly fine to treat them as if they're their own special category of thing

sibber•15mo ago

they dont

Angius•15mo ago

Oh?

MODiX•15mo ago

Angius

REPL Result: Failure

struct S {}
S s = S();

struct S {}
S s = S();

Exception: CompilationErrorException

- Non-invocable member 'S' cannot be used like a method.

- Non-invocable member 'S' cannot be used like a method.

Compile: 403.426ms | Execution: 0.000ms | React with ❌ to remove this embed.

sibber•15mo ago

not like that just S s;

Angius•15mo ago

Ah, you mean S s itself won't be null yeah You're right

sibber•15mo ago

yup

333fred•15mo ago

They do You need to assign some value to the local or it won't allow you to access it Most commonly, this is with new

Aaron•15mo ago

they are https://discord.com/channels/143867839282020352/569261465463160900/1154168125332402207

MODiX•15mo ago

Aaron

REPL Result: Success

new int[5] is Array

new int[5] is Array

Result: bool

True

True

Quoted by

<@270457259065081856> from #void-spam (click here)

Compile: 313.457ms | Execution: 74.367ms | React with ❌ to remove this embed.

Aaron•15mo ago

arrays are as much of a class as any other class

sibber•15mo ago

wdym

333fred•15mo ago

Definite assignment applies to structs just as much as it applies to classes

MODiX•15mo ago

Cyberrex

REPL Result: Success

S s;
s.i = 5;
struct S
{
     public int i;
}

S s;
s.i = 5;
struct S
{
     public int i;
}

Compile: 502.304ms | Execution: 31.011ms | React with ❌ to remove this embed.

333fred•15mo ago

Remember that the repl isn't doing what you think it is

sibber•15mo ago

huh

Aaron•15mo ago

it essentially makes s a field to see the actual rules, you have to make a method inside the repl

MODiX•15mo ago

Aaron

REPL Result: Success

void M() {
S s;
s.i = 5;
}
M();
struct S
{
     public int i;
}

void M() {
S s;
s.i = 5;
}
M();
struct S
{
     public int i;
}

Compile: 526.570ms | Execution: 34.776ms | React with ❌ to remove this embed.

sibber•15mo ago

this compiles in a normal app as well

Aaron•15mo ago

MODiX•15mo ago

333fred

REPL Result: Failure

void M() {
S s;
_ = s.i;
}
M();
struct S
{
     public int i;
}

void M() {
S s;
_ = s.i;
}
M();
struct S
{
     public int i;
}

Exception: CompilationErrorException

- Use of possibly unassigned field 'i'

- Use of possibly unassigned field 'i'

Compile: 529.253ms | Execution: 0.000ms | React with ❌ to remove this embed.

sibber•15mo ago

it even makes a suggestion if you new it

333fred•15mo ago

You need to definitely assign before you can use it

sibber•15mo ago

oh before you read yeah

Aaron•15mo ago

I didn't know the definite assignment rules treated struct fields independently

333fred•15mo ago

This suggestion is s = new() { i = 5 };

sibber•15mo ago

oh right lol nevermind that

Aaron•15mo ago

I suppose it makes sense to do so

333fred•15mo ago

Anyway, this is all way above the head of the original question. For simplicity's sake: you need to assign some value to any variable before you can use it

sibber•15mo ago

yeah so one field can be uninitialized while another can be initialized

Accord•15mo ago

Was this issue resolved? If so, run /close - otherwise I will mark this as stale and this post will be archived until there is new activity.

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❔ why new is needed for reference types