JsonSerializer improvements in .NET 5

[layomia]

In 5.0, we have added new features to JsonSerializer, improved performance and reliability, and made the serializer work on more platforms. This list goes over the most user-facing improvements.

Issue	Description	Category
#30820	Add mechanism to preserve object references when (de)serializing	Feature
#32937	Add extension methods for HttpClient that allow (de)serializing JSON	Feature
#30255	Support (de)serializing quoted numbers	Feature
#29895	Support deserializing objects using parameterized constructors	Feature
#876	Support (de)serializing fields	Feature
#779	Support ignoring value-type defaults	Feature
#30687	Support conditionally ignoring properties (always, never, when null/default)	Feature
#30524	Support non-string dictionary keys	Feature
#29743	Allow using non-public property accessors for (de)serialization	Feature
#34439	Provide opt-in for custom converters to handle null	Feature
#38539	Support new C# record types	Feature
#30445	Add a copy constructor to JsonSerializerOptions	Feature
#34626	Add constructor to JsonSerializerOptions that takes serialization defaults	Feature
#2259	Improve (de)serialization performance for collections	Performance
#36635	Improve serialization performance for small or value-type POCOS (TechEmpower)	Performance
#35848	Improve deserialization perf for case-insensitive and missing-property cases	Performance
dotnet/corefx#41845	Improve perf for serializing long JSON strings	Performance
#31326	Enable JsonSerializer to work on Xamarin iOS/Android	Platform support

Check out demos for the new features: https://github.com/layomia/NET5JsonDemos.

[Joelius300]

I'm guessing this list is complete and there won't be any other features added to the serializer until after .NET 5.0 is released, is that correct?

[layomia]

@Joelius300 yes, this list is complete. No other features will be added until after .NET 5.0 is released.

[TonyValenti]

With Records now part of C#, I think that the next release should include serialization/Deserialization for the immutable collections. I feel incomplete without it.

[layomia]

@TonyValenti - do you mean collections in System.Collections.Immutable (already supported), or generally probing for constructors that take IEnumerable<T>, T[], IEnumerable<KeyValuePair<TKey, TValue>>, etc.? Please feel free to open an issue describing your scenario.

[layomia]

Closing this issue as the feature work for System.Text.Json in 5.0 is complete.