using System;

using System.IO;

using System.Runtime.CompilerServices;

​

public static class Program {

    public static void Main() {

        TextWriter.Null.WriteInterpolated($"Hei på deg {123}"); 

    }

}

​

public static class TextWriterExtensions {

    public static TextWriter WriteInterpolated(this TextWriter writer, [InterpolatedStringHandlerArgument(nameof(writer))] ref WriteInterpolatedStringHandler handler) => writer;

​

    [InterpolatedStringHandler]

    public readonly struct WriteInterpolatedStringHandler {

        private readonly TextWriter _writer;

​

        public WriteInterpolatedStringHandler(int literalLength, int formattedCount, TextWriter writer, out bool isEnabled) {

            isEnabled = !ReferenceEquals(writer, TextWriter.Null);

            _writer = writer;

        }

​

        public void AppendLiteral(string value) {

            Console.WriteLine($"AppendLiteral: {value}");

            _writer.Write(value);

        }

​

        public void AppendFormatted<T>(T value) {

            if (value is not null) {

                Console.WriteLine($"AppendFormatted: {value}");

                _writer.Write(value.ToString());

            }

        }

    }

}