C#•2mo ago

✅ What is a primary constructor in C#

Hello guys, was just reading a bit about primary constructors. My question is, primary constructors is just a "fancy" way to write less code instead of declaring a whole constructor? Or are there any reasons why we would use primary constructors?

16 Replies

Thinker•2mo ago

Yes, primary constructors are literally just a simpler way to write normal constructors. These two are literally equivalent

class Person(string name, int age)
{
    public string Name { get; } = name;
    public int Age { get; } = age;
}

class Person(string name, int age)
{
    public string Name { get; } = name;
    public int Age { get; } = age;
}

class Person
{
    public string Name { get; }
    public int Age { get; }

    public Person(int name, int age)
    {
        Name = name;
        Age = age;
    }
}

class Person
{
    public string Name { get; }
    public int Age { get; }

    public Person(int name, int age)
    {
        Name = name;
        Age = age;
    }
}

If the constructor is public and you don't need any kind of functionality in the constructor besides initializing data, then a primary constructor is the same.

FakerOP•2mo ago

yep I see

Thinker•2mo ago

-# There are some slight nuances, but those are quite fringe.

Angius•2mo ago

Now, mind you, what the primary ctor generates can differ Depending on where you capture those params

FakerOP•2mo ago

yeah the idea of backing field, etc ?

Angius•2mo ago

But most of the time it doesn't really matter ye

Thinker•2mo ago

oh yeah, right, you can reference the parameters from the primary constructor elsewhere in the class eg. you can do this

class Foo(int num)
{
    public void PrintNum()
    {
        Console.WriteLine(num);
    }
}

class Foo(int num)
{
    public void PrintNum()
    {
        Console.WriteLine(num);
    }
}

FakerOP•2mo ago

yeah I see, yeah I see, hmm, consider the code: when we use primary constructors, like here:

C#
class Person(string name, int age)
{
    public string Name { get; } = name;
    public int Age { get; } = age;
}

C#
class Person(string name, int age)
{
    public string Name { get; } = name;
    public int Age { get; } = age;
}

the syntax is to set the variable "name" used in the primary constructors to the property "Name"?

Thinker•2mo ago

Reverse, the property Name is set to the parameter name

FakerOP•2mo ago

yeah sorry

Angius•2mo ago

You can always use Sharplab to see what gets generated

FakerOP•2mo ago

yeah I see

Thinker•2mo ago

Mind you again that primary constructors in records actually declare properties, which primary constructors in normal classes do not

Angius•2mo ago

And that nobody really writes record class when you can use just record 😛

Thinker•2mo ago

in record L(string Z);, Z will become a property, but in class L(string z); you'll get an empty class with just a constructor It's somewhat odd, but you don't need to worry about it too much unless you already know what records are.

FakerOP•2mo ago

just learning about that :c yep, I guess if I have some doubts, will just stick with sharplab to clearly see what's happening But I have an overview now, thanks guys 👍

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✅ What is a primary constructor in C#

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