FieldReferer

Field referer is an IRefererBase<Record, Field> that returns pointer to a field.

IReferer<MyClass, int> myClassIdReferer;
IRefererFromRef<MyStruct, int> myStructIdReferer;

Creating a referer

A simple referer implements just IWriterToRef<record,Field>.

IReferer<MyClass, int> myClassIdReferer = new MyClassIdReferer();
IRefererFromRef<MyStruct, int> myStructIdReferer = new MyStructIdReferer();

/// <summary></summary>
public class MyClassIdReferer : IReferer<MyClass, int>
{
    public bool CanRefer => true;
    public Type FromType => typeof(MyClass);
    public Type ToType => typeof(int);
    public ref int GetReference(MyClass record, IServiceProvider? context = null) => ref record.Id;
    public bool Accept(IWriterVisitorBase visitor) => visitor is not IRefererVisitor v ? true : v.Visit(refererT: this);
}

/// <summary></summary>
public class MyStructIdReferer : IRefererFromRef<MyStruct, int>
{
    public bool CanRefer => true;
    public Type FromType => typeof(MyStruct);
    public Type ToType => typeof(int);
    public ref int GetReference(ref MyStruct record, IServiceProvider? context = null) => ref record.Id;
    public bool Accept(IWriterVisitorBase visitor) => visitor is not IRefererVisitor v ? true : v.Visit(refererTFR: this);
}

FieldRefererRequest(IFieldDescription) builds a referer from field description.

FieldInfo fi = typeof(MyClass).GetField("Id")!;
IFieldDescription fieldDescription = new FieldDescription().Read(fi).SetReadOnly();
FieldRefererRequest request = new FieldRefererRequest(fieldDescription);
IRefererBase<MyClass, int> myClassIdReferer = AccessorServices.Instance.GetRequired<FieldRefererRequest, IRefererBase<MyClass, int>>(request);

Usage

Referer get pointer to a field of a record.

MyClass myClass = new MyClass(6, "");
ref int id = ref myClassIdReferer.GetReference(myClass);
MyStruct myStruct = new MyStruct(7, "");
ref int id2 = ref myStructIdReferer.GetReference(ref myStruct);

Custom referer builder

Custom handler can front-run FieldRefererRequest request.

public class MyClassIdRefererBuilder : IHandler<FieldRefererRequest, IWriterBase>
{
    [Order(-100)]
    public void Handle(IQuery<FieldRefererRequest, IWriterBase> query)
    {
        // Already handled
        if (query.Handled()) return;

        // 
        if (query.Request.Target is not IFieldDescription fieldDescription) return;
        // Get record type
        Type recordType = fieldDescription.Record?.Type ?? (fieldDescription.Referer as MemberInfo)?.DeclaringType!;
        // This handler only handles "MyClass"
        if (!typeof(MyClass).Equals(recordType)) return;
        //
        if (!"Id".Equals(fieldDescription.Name?.ToString())) return;
        // Create referer
        IWriterBase referer = new MyClassIdReferer();
        // Assign referer
        query.Response.SetValue(referer);
    }
}

// Create service
IService service = Services.Create((AccessorServices.Handlers, new MyClassIdRefererBuilder()), CachePolicies.Default);
// Create field description
IFieldDescription fieldDescription = new FieldDescription().Read(typeof(MyClass).GetField("Id")!).SetReadOnly();
// Referer request
FieldRefererRequest request = new FieldRefererRequest(fieldDescription);
// Get referer
IReferer<MyClass, int> myClassIdReferer = service.GetRequired<FieldRefererRequest, IReferer<MyClass, int>>(request);
// Create class
MyClass myClass = new MyClass(6, "");
// Read
ref int id = ref myClassIdReferer.GetReference(myClass);

Full Example

Full Example

Full example

using System;
using System.Reflection;
using Avalanche.Accessor;
using Avalanche.Service;
using Avalanche.Utilities;
using Avalanche.Utilities.Record;
using Avalanche.Writer;

public class fieldreferer
{
    // <00>
    public class MyClass
    {
        public int Id;
        public string Label;

        public MyClass(int id, string label)
        {
            Id = id;
            Label = label;
        }
    }

    public struct MyStruct
    {
        public int Id;
        public string Label;

        public MyStruct(int id, string label)
        {
            Id = id;
            Label = label;
        }
    }
    // </00>

    public static void Run()
    {
        {
#pragma warning disable CS0168
            // <01>
            IReferer<MyClass, int> myClassIdReferer;
            IRefererFromRef<MyStruct, int> myStructIdReferer;
            // </01>
#pragma warning restore CS0168
        }
        {
            // <11>
            //var myClassIdReferer = DelegateWriter.Referer((MyClass record) => record.Id);
            //var myStructIdReferer = DelegateWriter.Referer((MyStruct record) => record.Id);
            // </11>
        }
        {
            // <12>
            IReferer<MyClass, int> myClassIdReferer = new MyClassIdReferer();
            IRefererFromRef<MyStruct, int> myStructIdReferer = new MyStructIdReferer();
            // </12>
        }

        {
            // <17>
            FieldInfo fi = typeof(MyClass).GetField("Id")!;
            IFieldDescription fieldDescription = new FieldDescription().Read(fi).SetReadOnly();
            FieldRefererRequest request = new FieldRefererRequest(fieldDescription);
            IRefererBase<MyClass, int> myClassIdReferer = AccessorServices.Instance.GetRequired<FieldRefererRequest, IRefererBase<MyClass, int>>(request);
            // </17>
        }
        {
            FieldInfo fi = typeof(MyStruct).GetField("Id")!;
            IFieldDescription myStructDescription = new FieldDescription().Read(fi).SetReadOnly();
            FieldRefererRequest myStructRequest = new FieldRefererRequest(myStructDescription);
            IRefererBase<MyStruct, int> myStructIdReferer = AccessorServices.Instance.GetRequired<FieldRefererRequest, IRefererBase<MyStruct, int>>(myStructRequest);
        }


        {
            IReferer<MyClass, int> myClassIdReferer = new MyClassIdReferer();
            IRefererFromRef<MyStruct, int> myStructIdReferer = new MyStructIdReferer();

            // <21>
            MyClass myClass = new MyClass(6, "");
            ref int id = ref myClassIdReferer.GetReference(myClass);
            MyStruct myStruct = new MyStruct(7, "");
            ref int id2 = ref myStructIdReferer.GetReference(ref myStruct);
            // </21>
        }

        {
            // <32>
            // Create service
            IService service = Services.Create((AccessorServices.Handlers, new MyClassIdRefererBuilder()), CachePolicies.Default);
            // Create field description
            IFieldDescription fieldDescription = new FieldDescription().Read(typeof(MyClass).GetField("Id")!).SetReadOnly();
            // Referer request
            FieldRefererRequest request = new FieldRefererRequest(fieldDescription);
            // Get referer
            IReferer<MyClass, int> myClassIdReferer = service.GetRequired<FieldRefererRequest, IReferer<MyClass, int>>(request);
            // Create class
            MyClass myClass = new MyClass(6, "");
            // Read
            ref int id = ref myClassIdReferer.GetReference(myClass);
            // </32>
        }
    }

    // <13>
    /// <summary></summary>
    public class MyClassIdReferer : IReferer<MyClass, int>
    {
        public bool CanRefer => true;
        public Type FromType => typeof(MyClass);
        public Type ToType => typeof(int);
        public ref int GetReference(MyClass record, IServiceProvider? context = null) => ref record.Id;
        public bool Accept(IWriterVisitorBase visitor) => visitor is not IRefererVisitor v ? true : v.Visit(refererT: this);
    }

    /// <summary></summary>
    public class MyStructIdReferer : IRefererFromRef<MyStruct, int>
    {
        public bool CanRefer => true;
        public Type FromType => typeof(MyStruct);
        public Type ToType => typeof(int);
        public ref int GetReference(ref MyStruct record, IServiceProvider? context = null) => ref record.Id;
        public bool Accept(IWriterVisitorBase visitor) => visitor is not IRefererVisitor v ? true : v.Visit(refererTFR: this);
    }
    // </13>
    // <31>
    public class MyClassIdRefererBuilder : IHandler<FieldRefererRequest, IWriterBase>
    {
        [Order(-100)]
        public void Handle(IQuery<FieldRefererRequest, IWriterBase> query)
        {
            // Already handled
            if (query.Handled()) return;

            // 
            if (query.Request.Target is not IFieldDescription fieldDescription) return;
            // Get record type
            Type recordType = fieldDescription.Record?.Type ?? (fieldDescription.Referer as MemberInfo)?.DeclaringType!;
            // This handler only handles "MyClass"
            if (!typeof(MyClass).Equals(recordType)) return;
            //
            if (!"Id".Equals(fieldDescription.Name?.ToString())) return;
            // Create referer
            IWriterBase referer = new MyClassIdReferer();
            // Assign referer
            query.Response.SetValue(referer);
        }
    }
    // </31>
}