What is the positional syntax for property definition in C# 9.0?

Records in C# 9.0 provide positional syntax to declare and initialize property values of an instance.

The compiler makes the properties public init-only auto-implemented when the user employs positional syntax to declare and initialize properties.

The compiler also creates a constructor that accepts values and assigns them to properties according to their position. Additionally, a deconstruct method with an out parameter for each positional parameter is created when there are more than two positional properties.

Example

The following example demonstrates how to use the positional syntax for property definition with C# 9.0 records.

Example 1

The following code creates a record Course and initializes the init-only properties without an explicit constructor, using the positional syntax.

using System;
namespace Educative
{
	// create record
	public record Course(string Name , int Price );
	
    class positionalProperty
    {
        static void Main(string[] args)
        {
			//initialize using positonal syntax 
            var course = new Course("Intro to programming", 35);
			Console.WriteLine( course );
            
        }
    }
}

Output

Course { Name = Intro to programming, Price = 35 }

Example 2

If the user does not want the auto-implemented property definition, they can define the property themselves. The constructor and deconstructor then utilize the user’s property definition. The following example sets the Name property as protected instead of public.

using System;
namespace Educative
{
	// create record
	public record Course(string Name , int Price )
	{
		protected string Name { get; init; } = Name;
	}
	
    class positionalProperty
    {
        static void Main(string[] args)
        {
			//initialize using positonal syntax 
            var course = new Course("Intro to programming", 35);
			Console.WriteLine( course );
            
        }
    }
}

Output

Course { Price = 35 }
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