C#•6mo ago

When should i use Private constractor with factory method?

here included example

c#
public class Student
{

    private string name;
    private Student(string  name) 
    {
        this.name = name;
    }

    public static Student CreateObject(string name) 
    {
        return new Student(name);
    }

    public string Name 
    {
        get { return name; }
    }


}

c#
public class Student
{

    private string name;
    private Student(string  name) 
    {
        this.name = name;
    }

    public static Student CreateObject(string name) 
    {
        return new Student(name);
    }

    public string Name 
    {
        get { return name; }
    }


}

7 Replies

Angius•6mo ago

Most often, when you need some async work done on construction For example,

public class Classroom
{
    public List<Student> Students { get; private set; }

    private Student(List<Student> students)
    {
        Students = students;
    }

    public static async Task<Classroom> CreateInstance()
    {
        var data = await File.ReadAllTextAsync("students.json");
        var students = JsonSerializer.Deserialize<List<Student>>(data);
        return new Classroom(students);
    }
}

public class Classroom
{
    public List<Student> Students { get; private set; }

    private Student(List<Student> students)
    {
        Students = students;
    }

    public static async Task<Classroom> CreateInstance()
    {
        var data = await File.ReadAllTextAsync("students.json");
        var students = JsonSerializer.Deserialize<List<Student>>(data);
        return new Classroom(students);
    }
}

Other than that, it's done when some heavier work needs to be done before the instance is complete. Constructors, ideally, should be very simple and lightweight So it makes sense, ideologically, to have heavy work done in a factory

steven preadlyOP•6mo ago

this is an advanced topic for me now as a biggner

Angius•6mo ago

Yes, static factories are not something you would use often It's not something a beginner should be concerned with much

steven preadlyOP•6mo ago

but its ok to just have the infrmation correct

Angius•6mo ago

Sure

steven preadlyOP•6mo ago

ok thank you

SleepWellPupper•6mo ago

2cents: Constructors should be - simple - fast [citation needed] My rule of thumb is that if the initialization of objects is rather complicated / async (as mentioned) / or requires stuff that is transformed into what the object actually needs, then I use factory methods.

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When should i use Private constractor with factory method?