FSharpOptionConverter.cs

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using System.Diagnostics.CodeAnalysis;
using System.Text.Json.Serialization.Metadata;
 
namespace System.Text.Json.Serialization.Converters;
 
internal sealed class FSharpOptionConverter<TOption, TElement> : JsonConverter<TOption> where TOption : class
{
    private readonly JsonConverter<TElement> _elementConverter;
 
    private readonly Func<TOption, TElement> _optionValueGetter;
 
    private readonly Func<TElement, TOption> _optionConstructor;
 
    private readonly ConverterStrategy _converterStrategy;
 
    internal override ConverterStrategy ConverterStrategy => _converterStrategy;
 
    internal override Type ElementType => typeof(TElement);
 
    public override bool HandleNull => true;
 
    [RequiresUnreferencedCode("Uses Reflection to access FSharp.Core components at runtime.")]
    public FSharpOptionConverter(JsonConverter<TElement> elementConverter)
    {
        _elementConverter = elementConverter;
        _optionValueGetter = FSharpCoreReflectionProxy.Instance.CreateFSharpOptionValueGetter<TOption, TElement>();
        _optionConstructor = FSharpCoreReflectionProxy.Instance.CreateFSharpOptionSomeConstructor<TOption, TElement>();
        _converterStrategy = _elementConverter.ConverterStrategy;
        base.CanUseDirectReadOrWrite = _converterStrategy == ConverterStrategy.Value;
    }
 
    internal override bool OnTryRead(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options, ref ReadStack state, out TOption value)
    {
        if (!state.IsContinuation && reader.TokenType == JsonTokenType.Null)
        {
            value = null;
            return true;
        }
        state.Current.JsonPropertyInfo = state.Current.JsonTypeInfo.ElementTypeInfo.PropertyInfoForTypeInfo;
        if (_elementConverter.TryRead(ref reader, typeof(TElement), options, ref state, out var value2))
        {
            value = _optionConstructor(value2);
            return true;
        }
        value = null;
        return false;
    }
 
    internal override bool OnTryWrite(Utf8JsonWriter writer, TOption value, JsonSerializerOptions options, ref WriteStack state)
    {
        if (value == null)
        {
            writer.WriteNullValue();
            return true;
        }
        TElement value2 = _optionValueGetter(value);
        state.Current.DeclaredJsonPropertyInfo = state.Current.JsonTypeInfo.ElementTypeInfo.PropertyInfoForTypeInfo;
        return _elementConverter.TryWrite(writer, in value2, options, ref state);
    }
 
    public override void Write(Utf8JsonWriter writer, TOption value, JsonSerializerOptions options)
    {
        if (value == null)
        {
            writer.WriteNullValue();
            return;
        }
        TElement value2 = _optionValueGetter(value);
        _elementConverter.Write(writer, value2, options);
    }
 
    public override TOption Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
    {
        if (reader.TokenType == JsonTokenType.Null)
        {
            return null;
        }
        TElement arg = _elementConverter.Read(ref reader, typeToConvert, options);
        return _optionConstructor(arg);
    }
}