Introduction

IWriterBase is root interface for writers consumers.

/// <summary>Root interface for writers.</summary>
public interface IWriter 
{
    /// <summary>The most specific type this writer reads from.</summary>
    Type FromType { get; }
    /// <summary>The most specific type this writer writes to.</summary>
    Type ToType { get; }
}

/// <summary>Indicates that writer can write from <typeparamref name="From"/>.</summary>
public interface IWriterFrom<From> : IWriter { }
/// <summary>Indicates that Writer can write into <typeparamref name="To"/>.</summary>
public interface IWriterTo<To> : IWriter { }
/// <summary>Indicates that implements one of <see cref="IWriter{From, To}"/>, <see cref="IWriterFromRef{From, To}"/>, <see cref="IWriterToRef{From, To}"/> or <see cref="IWriterFromRefToRef{From, To}"/>.</summary>
public interface IWriterBase<From, To> : IWriterFrom<From>, IWriterTo<To> { }

/// <summary>Writes <typeparamref name="From"/> data to <typeparamref name="To"/>.</summary>
/// <typeparam name="From">Value to write</typeparam>
/// <typeparam name="To">Record/Container</typeparam>
public interface IWriter<From, To> : IWriterBase<From, To>
{
    /// <summary>Can write.</summary>
    /// <remarks>This property is needed for decoration layering.</remarks>
    bool CanWrite { get; }

    /// <summary>Try write <paramref name="from"/> to container in <paramref name="to"/>.</summary>
    /// <param name="from">source where content is read from.</param>
    /// <param name="to">target where write is written to. Structs and value types cannot be written to.</param>
    /// <returns>True if was write completed, false if write was not completed or supported.</returns>
    /// <exception cref="Exception">Unexpected error.</exception>
    bool TryWrite(From from, To to, IServiceProvider? context = null);
}

/// <summary>Writes <typeparamref name="From"/> data to <typeparamref name="To"/>.</summary>
/// <typeparam name="From">Value to write</typeparam>
/// <typeparam name="To">Record/Container</typeparam>
public interface IWriterFromRef<From, To> : IWriterBase<From, To>
{
    /// <summary>Can write</summary>
    /// <remarks>This property is needed for decoration layering.</remarks>
    bool CanWrite { get; }

    /// <summary>Try write <paramref name="from"/> to container in <paramref name="to"/>.</summary>
    /// <param name="from">source where content is read from.</param>
    /// <param name="to">target lass where content is written to. Structs and value types cannot be written to.</param>
    /// <returns>True if was write completed, false if write was not completed or supported.</returns>
    /// <exception cref="Exception">Unexpected error.</exception>
    bool TryWrite(ref From from, To to, IServiceProvider? context = null);
}

/// <summary>Writes <typeparamref name="From"/> data to <typeparamref name="To"/>.</summary>
/// <typeparam name="From">Value to write</typeparam>
/// <typeparam name="To">Record/Container</typeparam>
public interface IWriterToRef<From, To> : IWriterBase<From, To>
{
    /// <summary>Can write</summary>
    /// <remarks>This property is needed for decoration layering.</remarks>
    bool CanWrite { get; }

    /// <summary>Try write <paramref name="from"/> to container in <paramref name="to"/> or create new container if not available.</summary>
    /// <param name="from">source where content is read from.</param>
    /// <param name="to">target where write is written to. If 'null' then writer may create new container.</param>
    /// <returns>True if was write completed, false if write was not completed or supported.</returns>
    /// <exception cref="Exception">Unexpected error.</exception>
    bool TryWrite(From from, ref To to, IServiceProvider? context = null);
}

/// <summary>Writes <typeparamref name="From"/> data to <typeparamref name="To"/>.</summary>
/// <typeparam name="From">Value to write</typeparam>
/// <typeparam name="To">Record/Container</typeparam>
public interface IWriterFromRefToRef<From, To> : IWriterBase<From, To>
{
    /// <summary>Can write</summary>
    /// <remarks>This property is needed for decoration layering.</remarks>
    bool CanWrite { get; }

    /// <summary>Try write <paramref name="from"/> to container in <paramref name="to"/> or create new container if not available.</summary>
    /// <param name="from">source where content is read from.</param>
    /// <param name="to">target where write is written to. If 'null' then writer may create new container.</param>
    /// <returns>True if was write completed, false if write was not completed or supported.</returns>
    /// <exception cref="Exception">Unexpected error.</exception>
    bool TryWrite(ref From from, ref To to, IServiceProvider? context = null);
}

There are different ref versions of writer interface for different implementations.

IWriterBase
└── IWriterBase<From, To>
    ├── IWriter<From, To>
    ├── IWriterFromRef<From, To>
    ├── IWriterToRef<From, To>
    └── IWriterFromRefToRef<From, To>

The consumer of writer can use IWriterBase and extension methods that forward to correct implementation.

IWriter writer = new MyClassLabelWriter();
writer.WriteAs("Hello", instance);

IWriterBase<From, To> is another abstract interface for consumers.

IWriterBase<string, MyClass> writer = new MyClassLabelWriter();
writer.Write("Hello", instance);

Writer

Writer to class implements IWriter<From, To>.

IWriter<string, MyClass> writer = new MyClassLabelWriter();

Writer<From, To> base class can be used for implementations.

public class MyClassLabelWriter : Writer<string, MyClass>
{
    public override bool TryWrite(string from, MyClass to, IServiceProvider? context = null)
    {
        if (to == null) return false;
        to.Label = from;
        return true;
    }
}

Writer to struct implements IWriterToRef<From, To>.

IWriterToRef<string, MyStruct> writer = new MyStructLabelWriter();

public class MyStructLabelWriter : WriterToRef<string, MyStruct>
{
    public override bool TryWrite(string from, ref MyStruct to, IServiceProvider? context = null)
    {
        to.Label = from;
        return true;
    }
}

Writer can be adapted from delegate.

IWriter<string, MyClass> writer =
    DelegateWriter.Writer<string, MyClass>((string value, MyClass instance) => instance.Label = value);

And for structs IWriterToRef<From, To>.

IWriterToRef<string, MyStruct> writer =
    DelegateWriter.Writer<string, MyStruct>((string value, ref MyStruct instance) => instance.Label = value);

Extension method .Write() forwards to .TryWrite() and throws StatusException with BadWriteNotSupported if return value is false.

// Create instance
MyClass instance = new MyClass { Label = "ABC" };
// Write
writer.Write("ZYX", instance);

// Create instance
MyStruct instance = new MyStruct { Label = "ABC" };
// Write
writer.Write("ZYX", ref instance);

If writer is IWriterBase then extension method .WriteAs()<From, To> can be used to forward to .TryWrite().

MyClass instance = new MyClass { Label = "ABC" };
IWriter writer = new MyClassLabelWriter();
writer.WriteAs<string, MyClass>("ZYX", instance);

Reader

Reader implements IWriterToRef<From, To> for class.

IWriterToRef<MyClass, string> reader = new MyClassLabelReader();

WriterToRef<From, To> base class can be used for convenient implementations.

public class MyClassLabelReader : WriterToRef<MyClass, string>
{
    public override bool TryWrite(MyClass from, ref string to, IServiceProvider? context = null)
    {
        if (from == null) return false;
        to = from.Label;
        return true;
    }
}

Reader can be adapted from delegate.

IWriterToRef<MyClass, string> reader =
    DelegateWriter.Reader<MyClass, string>((MyClass @class) => @class.Label);

Extension method .Write() can be used for reading, though pointer to output must be provided with ref.

// Create instance
MyClass instance = new MyClass { Label = "ABC" };
// Write to here
string label = null!;
// Write from instance to stack frame
reader.Write(instance, ref label);

Extension method .Read() forwards to TryWrite().

// Write from instance to stack frame
label = reader.Read(instance);

If writer is IWriterBase then extension method .ReadAs()<From, To> forwars to the correct .TryWrite.

IWriter reader = new MyClassLabelReader();
string label = reader.ReadAs<MyClass, string>(instance);

Visitor

IWriterVisitor is the interface for writer visitor implementations. Invoked from IWriterVisitable.Accept(IWriterVisitor).

/// <summary>Visitable writer</summary>
public interface IWriterVisitable : IWriter
{
    /// <summary>Try accept <paramref name="visitor"/>. Visits all <see cref="IWriter{From, To}"/> types that are implemented.</summary>
    /// <returns>Return true if all visitors were visited (all returned true).</returns>
    bool Accept(IWriterVisitor visitor);
}

/// <summary>Writer visitor</summary>
public interface IWriterVisitor
{
    /// <summary>Try visit <paramref name="writerT"/>.</summary>
    /// <returns>true to continue visitation</returns>
    bool Visit<From, To>(IWriter<From, To> writerT);
    /// <summary>Try visit <paramref name="writerTFR"/>.</summary>
    /// <returns>true to continue visitation</returns>
    bool Visit<From, To>(IWriterFromRef<From, To> writerTFR);
    /// <summary>Try visit <paramref name="writerTTR"/>.</summary>
    /// <returns>true to continue visitation</returns>
    bool Visit<From, To>(IWriterToRef<From, To> writerTTR);
    /// <summary>Try visit <paramref name="writerTFRTR"/>.</summary>
    /// <returns>true to continue visitation</returns>
    bool Visit<From, To>(IWriterFromRefToRef<From, To> writerTFRTR);

    /// <summary>Try visit <paramref name="refererT"/>.</summary>
    /// <returns>true to continue visitation</returns>
    bool Visit<From, To>(IReferer<From, To> refererT) where From : notnull;
    /// <summary>Try visit <paramref name="refererTFR"/>.</summary>
    /// <returns>true to continue visitation</returns>
    bool Visit<From, To>(IRefererFromRef<From, To> refererTFR) where From : notnull;
}

Writer that implements IWriterBase accepts visitors.

IWriter reader = new MyClassLabelReader();
IWriterVisitor visitor = new MyVisitor();
(reader as IWriterVisitable)!.Accept(visitor);

public class MyVisitor : IWriterVisitor
{
    public bool Visit<From, To>(IWriter<From, To> writerT)
    { WriteLine($"IWriter<{typeof(From).Name},{typeof(To).Name}>"); return true; }
    public bool Visit<From, To>(IWriterFromRef<From, To> writerTFR)
    { WriteLine($"IWriter<{typeof(From).Name},{typeof(To).Name}>"); return true; }
    public bool Visit<From, To>(IWriterToRef<From, To> writerTTR)
    { WriteLine($"IWriter<{typeof(From).Name},{typeof(To).Name}>"); return true; }
    public bool Visit<From, To>(IWriterFromRefToRef<From, To> writerTFRTR)
    { WriteLine($"IWriter<{typeof(From).Name},{typeof(To).Name}>"); return true; }

    public bool Visit<From, To>(IReferer<From, To> refererT) where From : notnull
    { WriteLine($"IReferer<{typeof(From).Name},{typeof(To).Name}>"); return true; }
    public bool Visit<From, To>(IRefererFromRef<From, To> refererTFR) where From : notnull
    { WriteLine($"IRefererFromRef<{typeof(From).Name},{typeof(To).Name}>"); return true; }
}

The extension method .GetWriterToAndFromTypes() gets implemented from and to types.

List<KeyValuePair<Type, Type>> types = reader.GetWriterToAndFromTypes();

As do .GetWriterInterfaces().

List<Type> types = reader.GetWriterInterfaces();

And .GetWriterRefAndTypes().

List<(bool fromRef, Type fromType, bool toRef, Type toType)> types = reader.GetWriterRefAndTypes();

IWriterComposition

IWriterComposition interface exposes inner components for decorator implementations.

/// <summary>Exposes writer internal components.</summary>
public interface IWriterComposition : IWriter, IComposition<IWriter> { }

.PrintTree() extension method prints inner structure as tree.

IWriter reader = new MyClassLabelReader();
reader = WriterAdapter.Adapt(reader);
string tree = reader.PrintTree();

.VisitTree() extension method visits writer structure.

IWriter reader = new MyClassLabelReader();
reader = WriterAdapter.Adapt(reader);
foreach (var line in reader.VisitTree())
    WriteLine(line);

Full Example

Full example

using System;
using System.Collections.Generic;
using Avalanche.Service;
using Avalanche.Writer;
using static System.Console;

public class writer
{
    public static void Run()
    {
        {
            MyClass instance = new MyClass();
            // <01>
            IWriter writer = new MyClassLabelWriter();
            writer.WriteAs("Hello", instance);
            // </01>
        }
        {
            MyClass instance = new MyClass();
            // <02>
            IWriterBase<string, MyClass> writer = new MyClassLabelWriter();
            writer.Write("Hello", instance);
            // </02>
        }

        {
            // <W01>
            IWriter<string, MyClass> writer =
                DelegateWriter.Writer<string, MyClass>((string value, MyClass instance) => instance.Label = value);
            // </W01>
        }
        {
            // <W01B>
            IWriterToRef<string, MyStruct> writer =
                DelegateWriter.Writer<string, MyStruct>((string value, ref MyStruct instance) => instance.Label = value);
            // </W01B>
        }
        {
            // <W02>
            IWriter<string, MyClass> writer = new MyClassLabelWriter();
            // </W02>
        }
        {
            // <W02B>
            IWriterToRef<string, MyStruct> writer = new MyStructLabelWriter();
            // </W02B>
        }
        {
            IWriter<string, MyClass> writer = new MyClassLabelWriter();
            // <W04>
            // Create instance
            MyClass instance = new MyClass { Label = "ABC" };
            // Write
            writer.Write("ZYX", instance);
            // </W04>
        }
        {
            IWriterToRef<string, MyStruct> writer = new MyStructLabelWriter();
            // <W04B>
            // Create instance
            MyStruct instance = new MyStruct { Label = "ABC" };
            // Write
            writer.Write("ZYX", ref instance);
            // </W04B>
        }
        {
            // <W05>
            MyClass instance = new MyClass { Label = "ABC" };
            IWriter writer = new MyClassLabelWriter();
            writer.WriteAs<string, MyClass>("ZYX", instance);
            // </W05>
        }

        {
            // <R01>
            IWriterToRef<MyClass, string> reader =
                DelegateWriter.Reader<MyClass, string>((MyClass @class) => @class.Label);
            // </R01>
        }
        {
            // <R02>
            IWriterToRef<MyClass, string> reader = new MyClassLabelReader();
            // </R02>
        }
        {
            IWriterToRef<MyClass, string> reader = new MyClassLabelReader();
            // <R04>
            // Create instance
            MyClass instance = new MyClass { Label = "ABC" };
            // Write to here
            string label = null!;
            // Write from instance to stack frame
            reader.Write(instance, ref label);
            // </R04>
            // <R05>
            // Write from instance to stack frame
            label = reader.Read(instance);
            // </R05>
        }
        {
            MyClass instance = new MyClass { Label = "ABC" };
            // <R06>
            IWriter reader = new MyClassLabelReader();
            string label = reader.ReadAs<MyClass, string>(instance);
            // </R06>
        }

        {
            // <V00>
            IWriter reader = new MyClassLabelReader();
            IWriterVisitor visitor = new MyVisitor();
            (reader as IWriterVisitable)!.Accept(visitor);
            // </V00>
        }
        {
            IWriter reader = new MyClassLabelReader();
            // <V01>
            List<KeyValuePair<Type, Type>> types = reader.GetWriterToAndFromTypes();
            // </V01>
        }
        {
            IWriter reader = new MyClassLabelReader();
            // <V02>
            List<Type> types = reader.GetWriterInterfaces();
            // </V02>
        }
        {
            IWriter reader = new MyClassLabelReader();
            // <V03>
            List<(bool fromRef, Type fromType, bool toRef, Type toType)> types = reader.GetWriterRefAndTypes();
            // </V03>
        }
        {
            // <C04>
            IWriter reader = new MyClassLabelReader();
            reader = WriterAdapter.Adapt(reader);
            string tree = reader.PrintTree();
            // </C04>
            WriteLine(tree);
        }
        {
            // <C05>
            IWriter reader = new MyClassLabelReader();
            reader = WriterAdapter.Adapt(reader);
            foreach (var line in reader.VisitTree())
                WriteLine(line);
            // </C05>
        }

    }

    // <00>
    public class MyClass
    {
        public string Label = null!;
    }
    public struct MyStruct
    {
        public string Label;
    }
    // </00>

    // <R03>
    public class MyClassLabelReader : WriterToRef<MyClass, string>
    {
        public override bool TryWrite(MyClass from, ref string to, IServiceProvider? context = null)
        {
            if (from == null) return false;
            to = from.Label;
            return true;
        }
    }
    // </R03>

    // <W03>
    public class MyClassLabelWriter : Writer<string, MyClass>
    {
        public override bool TryWrite(string from, MyClass to, IServiceProvider? context = null)
        {
            if (to == null) return false;
            to.Label = from;
            return true;
        }
    }
    // </W03>
    // <W03B>
    public class MyStructLabelWriter : WriterToRef<string, MyStruct>
    {
        public override bool TryWrite(string from, ref MyStruct to, IServiceProvider? context = null)
        {
            to.Label = from;
            return true;
        }
    }
    // </W03B>
    // <V06>
    public class MyVisitor : IWriterVisitor
    {
        public bool Visit<From, To>(IWriter<From, To> writerT)
        { WriteLine($"IWriter<{typeof(From).Name},{typeof(To).Name}>"); return true; }
        public bool Visit<From, To>(IWriterFromRef<From, To> writerTFR)
        { WriteLine($"IWriter<{typeof(From).Name},{typeof(To).Name}>"); return true; }
        public bool Visit<From, To>(IWriterToRef<From, To> writerTTR)
        { WriteLine($"IWriter<{typeof(From).Name},{typeof(To).Name}>"); return true; }
        public bool Visit<From, To>(IWriterFromRefToRef<From, To> writerTFRTR)
        { WriteLine($"IWriter<{typeof(From).Name},{typeof(To).Name}>"); return true; }

        public bool Visit<From, To>(IReferer<From, To> refererT) where From : notnull
        { WriteLine($"IReferer<{typeof(From).Name},{typeof(To).Name}>"); return true; }
        public bool Visit<From, To>(IRefererFromRef<From, To> refererTFR) where From : notnull
        { WriteLine($"IRefererFromRef<{typeof(From).Name},{typeof(To).Name}>"); return true; }
    }
    // </V06>
}