Constructors in C#

How an object insists on the data it cannot exist without.

var plain = new Circle(2.0);
var unit = new Circle(1.0, "unit");
Console.WriteLine($"{plain.Name}: {plain.Area:F2}");
Console.WriteLine($"{unit.Name}: {unit.Area:F2}");

class Circle
{
    public string Name { get; }
    public double Radius { get; }
    public double Area => Math.PI * Radius * Radius;

    public Circle(double radius, string name = "circle")
    {
        Radius = radius;
        Name = name;
    }
}

How it works

1. The constructor takes radius and an optional name.
2. Get-only properties are assigned there and never again.
3. Area is computed on demand from Radius, not stored.

Keywords and builtins used here

• Circle
• class
• double
• get
• new
• public
• string
• var

The run, in numbers

Lines

17

Characters to type

381

Tokens

85

Three-star pace

85 tpm

At the three-star pace of 85 tokens a minute, this run takes about 60 seconds.

Type this snippet

Step 2 of 4 in Classes & records, step 19 of 29 in Language basics.

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