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// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
using System.Collections.Generic;
using System.Diagnostics;
namespace System.Text.Json.Serialization.Converters
{
/// Converter for <cref>System.Collections.Generic.List{TElement}</cref>.
internal sealed class ListOfTConverter<TCollection, TElement>
: IEnumerableDefaultConverter<TCollection, TElement>
where TCollection : List<TElement>
{
internal override bool CanPopulate => true;
protected override void Add(in TElement value, ref ReadStack state)
{
((TCollection)state.Current.ReturnValue!).Add(value);
}
protected override void CreateCollection(ref Utf8JsonReader reader, scoped ref ReadStack state, JsonSerializerOptions options)
{
if (state.ParentProperty?.TryGetPrePopulatedValue(ref state) == true)
{
return;
}
if (state.Current.JsonTypeInfo.CreateObject == null)
{
ThrowHelper.ThrowNotSupportedException_SerializationNotSupported(state.Current.JsonTypeInfo.Type);
}
state.Current.ReturnValue = state.Current.JsonTypeInfo.CreateObject();
}
protected override bool OnWriteResume(Utf8JsonWriter writer, TCollection value, JsonSerializerOptions options, ref WriteStack state)
{
List<TElement> list = value;
// Using an index is 2x faster than using an enumerator.
int index = state.Current.EnumeratorIndex;
JsonConverter<TElement> elementConverter = GetElementConverter(ref state);
if (elementConverter.CanUseDirectReadOrWrite && state.Current.NumberHandling == null)
{
// Fast path that avoids validation and extra indirection.
for (; index < list.Count; index++)
{
elementConverter.Write(writer, list[index], options);
}
}
else
{
for (; index < list.Count; index++)
{
TElement element = list[index];
if (!elementConverter.TryWrite(writer, element, options, ref state))
{
state.Current.EnumeratorIndex = index;
return false;
}
state.Current.EndCollectionElement();
if (ShouldFlush(ref state, writer))
{
state.Current.EnumeratorIndex = ++index;
return false;
}
}
}
return true;
}
}
}
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