C#•3mo ago

✅ what is a primary constructor? is it any similar to parameterless constructor?

the content provided on Microsoft Learn is confusing.

80 Replies

Are you familiar with records?

public record Example(string Name);

public record Example(string Name);

tommyOP•3mo ago

hey man!! how are you? not particularly

Pobiega•3mo ago

okay, lets ignore them for now then

tommyOP•3mo ago

do i have to know them in order to understand this

Pobiega•3mo ago

nope

tommyOP•3mo ago

okay

Pobiega•3mo ago

a primary constructor is just a different way of writing a constructor - but it then becomes the "primary" constructor that all other constructors must also use

public class Example(string name)
{
    public string Name { get; } = name;
}

public class Example(string name)
{
    public string Name { get; } = name;
}

simple example, the primary constructor takes in a single string name that we use to initialize a property.

tommyOP•3mo ago

hold on so we define it along with the class name and there's a parameter available throughout the scope of the class that is provided inside that constructor

Pobiega•3mo ago

yes

tommyOP•3mo ago

okay! now let's get to the second part when you say

Pobiega•3mo ago

okay, lets introduce a non-primary constructor here

tommyOP•3mo ago

"all other constructor must also use"

Pobiega•3mo ago

public class Example(string name)
{
    public string Name { get; } = name;

    // parameterless constructor
    public Example() : this("Default")
    {
    }

    public Example(string name, int age) : this(name)
    {
        Age = age;
    }

    public int Age { get; private set; }
}

public class Example(string name)
{
    public string Name { get; } = name;

    // parameterless constructor
    public Example() : this("Default")
    {
    }

    public Example(string name, int age) : this(name)
    {
        Age = age;
    }

    public int Age { get; private set; }
}

here we have the same class but with 2 alternative constructors

tommyOP•3mo ago

okay!

Pobiega•3mo ago

we add a parameterless one, that just sets the name to a default value, and one that also sets an age they must call this(string) or the compiler will be angry

tommyOP•3mo ago

so, here, this refers to the primary constructor? i mean this

Pobiega•3mo ago

yes its not different from constructor overloading in general, except that its a must here

tommyOP•3mo ago

okay! so you gotta have a parameterless constructor inside the class

Pobiega•3mo ago

no? I just added that as an example

tommyOP•3mo ago

then why does the compiler get angry

Pobiega•3mo ago

tommyOP•3mo ago

oh i see!

Pobiega•3mo ago

the primary constructor is primary

tommyOP•3mo ago

every constructor must use the primary constructor

Pobiega•3mo ago

you cant skip invoking it yes or use one that uses it, iirc

tommyOP•3mo ago

so there doesn't have to be a primary constructor but if there is one, every other constructor must follow it

Pobiega•3mo ago

yes primary ctors are optional.

tommyOP•3mo ago

what if i make the primary constructor that is parameterless

Pobiega•3mo ago

thats the default. its called "not having a primary constructor" 😛

tommyOP•3mo ago

same thing goes for it as well?

Pobiega•3mo ago

note how the primary constructor cant have a body, it just has parameters

tommyOP•3mo ago

does it have to have them?

Pobiega•3mo ago

so if you want a parameterless constructor with a body, just make a normal constructor I mean, what is a parameter less primary constructor? its literally nothing

tommyOP•3mo ago

yeah!

Pobiega•3mo ago

primary ctors do one thing and ONE THING ONLY: they specify parameters so a parameterless primary ctor is... pointless

tommyOP•3mo ago

very quirky question but, do we still have to follow the this() protocol even when the primary constructor is paramterless? yeah i get it

Unknown User•3mo ago

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Pobiega•3mo ago

Unknown User•3mo ago

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tommyOP•3mo ago

sorry i had to go to pee yeah so having an empty primary constructor is not possible then, right? i think weird questions do help us better understand the language

Pobiega•3mo ago

it is, but its useless

public class Example()
{
    public string Name { get; }
}

public class Example()
{
    public string Name { get; }
}

this is valid, but why bother? just confuses people

tommyOP•3mo ago

got it one more thing are the get and set access methods public by default

Unknown User•3mo ago

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tommyOP•3mo ago

okay

Unknown User•3mo ago

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tommyOP•3mo ago

yeah i saw this earlier

Unknown User•3mo ago

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tommyOP•3mo ago

from pobiega

Unknown User•3mo ago

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tommyOP•3mo ago

ookay

Unknown User•3mo ago

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tommyOP•3mo ago

ohhh

Unknown User•3mo ago

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tommyOP•3mo ago

got it

Unknown User•3mo ago

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tommyOP•3mo ago

i haven't yet got to async and await but the rest of the thing

Unknown User•3mo ago

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tommyOP•3mo ago

i understood that was a really helpful discussion thank you

Unknown User•3mo ago

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tommyOP•3mo ago

i will have to learn that first lol thank you to both @TeBeCo and @Pobiega

Pobiega•3mo ago

tommyOP•3mo ago

this does not seem to be the case i tried but the property remains private i think or maybe i am wrong idk

Unknown User•3mo ago

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tommyOP•3mo ago

ohhh got it it does not have a setter shit

MODiX•3mo ago

TeBeCo

REPL Result: Success

var foo = Foo.Create();
Console.WriteLine(foo.Name);

public class Foo
{
  internal Foo() {}

  public string Name { get; } = "bla";

  public static Foo Create() => new();
}

var foo = Foo.Create();
Console.WriteLine(foo.Name);

public class Foo
{
  internal Foo() {}

  public string Name { get; } = "bla";

  public static Foo Create() => new();
}

Console Output

bla

bla

Compile: 496.598ms | Execution: 35.344ms | React with ❌ to remove this embed.

tommyOP•3mo ago

yeah my bad my bad sorry no i think it is man check this out

Unknown User•3mo ago

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tommyOP•3mo ago

as i hover over it in visual studio it says private

tommyOP•3mo ago

this is it there seems to be a problem here

Pobiega•3mo ago

uh yeah, thats private. members are by default private there is no problem, this is the expected behaviour

tommyOP•3mo ago

what is up with this compiler then

Pobiega•3mo ago

tommyOP•3mo ago

this is confusing it compiled

Pobiega•3mo ago

so? I dont see a problem the property is public

tommyOP•3mo ago

ohh okay

Pobiega•3mo ago

the constructor is internal, but called via a public static method

tommyOP•3mo ago

i thought there wasn't an access modifier got it!!

Unknown User•3mo ago

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tommyOP•3mo ago

got it!!

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✅ what is a primary constructor? is it any similar to parameterless constructor?