IBufferWriter.cs

using System;
using System.Buffers;
using System.Runtime.CompilerServices;
using BenchmarkDotNet.Attributes;
using BenchmarkDotNet.Running;

public class Program
{
    public static void Main(string[] args)
        => BenchmarkSwitcher.FromAssembly(typeof(Program).Assembly).Run(args);

    private BufferWriter _writer = new BufferWriter();

    [Benchmark()]
    public void WriterGenericWrapper()
    {
        var writer = GetWriter(_writer);
        writer.Advance(1);
        writer.GetMemory();
        writer.GetSpan();
    }

    [Benchmark()]
    public void WriterGeneric()
    {
        var writer = new Writer<BufferWriter>(_writer);
        writer.Advance(1);
        writer.GetMemory();
        writer.GetSpan();
    }


    [Benchmark()]
    public void WriterInterface()
    {
        var writer = new Writer(_writer);
        writer.Advance(1);
        writer.GetMemory();
        writer.GetSpan();
    }


    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    private static Writer<WriterAdapter> GetWriter(BufferWriter pipeWriter)
        => new Writer<WriterAdapter>(new WriterAdapter(pipeWriter));

    private struct WriterAdapter : IBufferWriter<byte>
    {
        public BufferWriter Writer;
        public WriterAdapter(BufferWriter writer) => Writer = writer;
        public void Advance(int count) => Writer.Advance(count);
        public Memory<byte> GetMemory(int sizeHint = 0) => Writer.GetMemory(sizeHint);
        public Span<byte> GetSpan(int sizeHint = 0) => Writer.GetSpan(sizeHint);
    }
}

public struct Writer<TBufferWriter>
    where TBufferWriter : IBufferWriter<byte>
{
    private TBufferWriter _writer;

    public Writer(TBufferWriter writer) => _writer = writer;
    public void Advance(int count) => _writer.Advance(count);
    public Memory<byte> GetMemory(int sizeHint = 0) => _writer.GetMemory(sizeHint);
    public Span<byte> GetSpan(int sizeHint = 0) => _writer.GetSpan(sizeHint);
}

public struct Writer
{
    private IBufferWriter<byte> _writer;

    public Writer(IBufferWriter<byte> writer) => _writer = writer;
    public void Advance(int count) => _writer.Advance(count);
    public Memory<byte> GetMemory(int sizeHint = 0) => _writer.GetMemory(sizeHint);
    public Span<byte> GetSpan(int sizeHint = 0) => _writer.GetSpan(sizeHint);
}

public class BufferWriter : IBufferWriter<byte>
{
    public void Advance(int count) { }
    public Memory<byte> GetMemory(int sizeHint = 0) => default;
    public Span<byte> GetSpan(int sizeHint = 0) => default;
}

// * Summary *

BenchmarkDotNet=v0.11.3, OS=Windows 10.0.18309
Intel Core i7-4720HQ CPU 2.60GHz (Haswell), 1 CPU, 8 logical and 4 physical cores
.NET Core SDK=3.0.100-preview-009820
  [Host]     : .NET Core 3.0.0-preview-27205-02 (CoreCLR 4.6.27204.02, CoreFX 4.7.18.60501), 64bit RyuJIT
  DefaultJob : .NET Core 3.0.0-preview-27205-02 (CoreCLR 4.6.27204.02, CoreFX 4.7.18.60501), 64bit RyuJIT


               Method |     Mean |     Error |    StdDev |
--------------------- |---------:|----------:|----------:|
 WriterGenericWrapper | 10.85 ns | 0.0098 ns | 0.0091 ns |
        WriterGeneric | 19.72 ns | 0.0492 ns | 0.0384 ns |
      WriterInterface | 19.73 ns | 0.0311 ns | 0.0260 ns |