Add in-place sorting methods to OrderedDictionary

[eiriktsarpalis]

Maybe it's worth adding more methods

public void Move(int oldIndex, int newIndex);
public void Sort(IComparer<TValue> comparer);

Originally posted by @kronic in #103309 (comment)

An in-place, stable sorting method in particular would be very useful in the context of using OrderedDictionary in System.Text.Json

cc @stephentoub

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[stephentoub]

would be very useful in the context of using OrderedDictionary in System.Text.Json

Can you point to where?

And would it actually need Move? It's quite possible the fastest implementation would just sort the Entry list and then throw away and recreate the buckets.

[eiriktsarpalis]

Can you point to where?

Sure:

runtime/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Metadata/JsonTypeInfo.cs

Line 1137 in 7e977dc

propertyCache.List.StableSortByKey(static propInfo => propInfo.Value.Order);

The List property of the current structure exposes the mutable List component for faster access.

[stephentoub]

And it'd be ok for it to not be a stable sort?

[eiriktsarpalis]

In this case stability is a requirement (it would change the semantics of the JsonPropertyOrderAttribute)

[eiriktsarpalis]

We could perhaps make stability opt-in by feeding the index into the comparer?

[stephentoub]

We could perhaps make stability opt-in by feeding the index into the comparer?

Then you couldn't use IComparer<T> or Comparison<T>, which would make this a very unusual API and it would force the dictionary to have its own complete sorting implementation top to bottom, rather than being able to use Array.Sort and friends (unless it does what LINQ does, which is allocate a copy of the original indices, allocate a new comparer that uses it, etc.)

[eiriktsarpalis]

An in-place stable sorting implementation is something we're sorely missing at the moment. We could start by adding it to array and span, then work our way up to List-like types.

[stephentoub]

An in-place stable sorting implementation is something we're sorely missing at the moment. We could start by adding it to array and span, then work our way up to List-like types.

I'm fine with that, but I wouldn't want to add this API until that existed, we figured out naming conventions, there was something for this to depend on and use, etc. You marked this as 9.0; will you be pushing for a stable sort up and down the stack for 9 as well?

[eiriktsarpalis]

Let's keep it as a suggestion for now.

[stephentoub]

We could still expose Move (and/or Swap) if that would be the deal breaker with STJ using this type in 9.