RecordArray - Reasonable ToString and comparison for sequences in records.

RecordArray.cs

using System.Collections;
using System.Text;
using System.Text.Json;
using System.Text.Json.Serialization;

namespace Shared
{
  partial class RecordArrayConverter<T> : JsonConverter<RecordArray<T>>
  {
    public RecordArrayConverter() {}

    public override bool CanConvert(Type typeToConvert) =>
      typeToConvert == typeof(RecordArray<T>)
      ;

    public override RecordArray<T> Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
    {
      var vs = JsonSerializer.Deserialize<T[]>(ref reader, options);
      return vs is not null ? new(vs) : default;
    }

    public override void Write(Utf8JsonWriter writer, RecordArray<T> value, JsonSerializerOptions options)
    {
      var vs = value._vs ?? Array.Empty<T>();
      JsonSerializer.Serialize(writer, vs, options);
    }
  }

  partial class RecordArrayConverter : JsonConverterFactory
  {
    public override bool CanConvert(Type typeToConvert) =>
      typeToConvert.GetGenericTypeDefinition() == typeof(RecordArray<>)
      ;

    public override JsonConverter? CreateConverter(Type typeToConvert, JsonSerializerOptions options)
    {
      if (typeToConvert.GetGenericTypeDefinition() != typeof(RecordArray<>))
      {
        throw new ArgumentException(
            $"Expected typeToConvert to be RecordArray<> but is {typeToConvert.Name}"
          , nameof(typeToConvert)
          );
      }

      var nested  = typeToConvert.GetGenericArguments()[0];
      var rac     = typeof(RecordArrayConverter<>).MakeGenericType(nested);
      var ctor    = rac.GetConstructor(Array.Empty<Type>());
      return (JsonConverter?)ctor?.Invoke(null);
    }
  }

  static partial class RecordArraysExtensions
  {
    public static RecordArray<T> ToRecordArray<T>(this T[]? vs) =>
      new(vs)
      ;

    public static RecordArray<T> ToRecordArray<T>(this IEnumerable<T>? vs) =>
      (vs?.ToArray()).ToRecordArray()
      ;
  }

  [JsonConverter(typeof(RecordArrayConverter))]
  partial struct RecordArray<T> 
    : IEquatable<RecordArray<T>>
    , IEnumerable<T>
    , IStructuralEquatable
    , IStructuralComparable
  {
    internal readonly T[]? _vs;

    public RecordArray(params T[]? vs)
    {
      _vs = vs;
    }

    public int Length
    {
      get
      {
        var vs = _vs;
        return vs is not null ? vs.Length : 0;
      }
    }

    public T this[int index]
    {
      get
      {
        var vs = _vs;
        return 
            vs is not null 
          ? vs[index] 
          : throw new IndexOutOfRangeException()
          ;
      }
    }

    public bool Equals(RecordArray<T> other)
    {
      var vs = _vs;
      var ovs = other._vs;

      if (vs is not null && ovs is not null)
      {
        IStructuralEquatable seq = vs;
        return seq.Equals(ovs, EqualityComparer<T>.Default);
      }
      else
      {
        return vs is null && ovs is null;
      }
    }

    public override bool Equals(object? other) =>
      other is RecordArray<T> ra && Equals(ra)
      ;

    public override int GetHashCode()
    {
      IStructuralEquatable seq = _vs ?? Array.Empty<T>();
      return seq.GetHashCode(EqualityComparer<T>.Default);
    }

    public override string ToString()
    {
      var sb = new StringBuilder(64);
      sb.Append("[");

      var vs = _vs;
      if (vs is not null)
      {
        var pre = "";
        foreach (var v in vs)
        {
          sb.Append(pre);
          sb.Append(v);
          pre = "; ";
        }
      }
      sb.Append("]");

      return sb.ToString();
    }

    public IEnumerator<T> GetEnumerator()
    {
      var vs = _vs;
      if (vs is not null)
      {
        foreach (var v in vs) yield return v;
      }
    }

    IEnumerator IEnumerable.GetEnumerator()
    {
      return GetEnumerator();
    }

    public bool Equals(object? other, IEqualityComparer comparer)
    {
      var vs = _vs ?? Array.Empty<T>();
      IStructuralEquatable seq = vs;
      return seq.Equals(other, comparer);
    }

    public int GetHashCode(IEqualityComparer comparer)
    {
      var vs = _vs ?? Array.Empty<T>();
      IStructuralEquatable seq = vs;
      return seq.GetHashCode(comparer);
    }

    public int CompareTo(object? other, IComparer comparer)
    {
      var vs = _vs ?? Array.Empty<T>();
      IStructuralComparable sc = vs;
      return sc.CompareTo(other, comparer);
    }
  }
}