Add useful minimal Functional Lenses implementation about imtools HOT 4 CLOSED

Lenses seems are hard as many relevant topics emerge:

• immutability and Dispose (custom X Dispose() with X X.Using(), not void Dispose() using(x){}). I.e. other mechanisms for memory management inside immutable tree (e.g. reference counting for some cache/pool/native pointers/ kernel handles/ file handles/ etc), not GC. These infect whole tree, mutable inside immutable?
• if have object tree better have it structural equality out of box for all of it.
• can tree use Ref wrappers around value tuples, around readonly structs? ref returns of structs from immutable tree? Stack only tree and it lenses (infinite loop handling evens and changing readonly struct stored on stack?
• default values not set? Options?
• could we have expression based lenses - allows for clever dependencies tracking, merge, diff, updates. see also https://github.com/louthy/language-ext/blob/e385e64c8c025b606640e4631c53d63bf27c2a58/LanguageExt.Core/DataTypes/Patch/Edit.cs
• how to notify about update our of immutable tree to show changes in UI (lenses with notify property changed)?
• Clone lense - sub tree or whole? Custom View onto immutable tree? View with custom lenses?
• when I balance tree, what API is best for less typing and less breaks when changing lenses?
• experience of F# lenses? https://xyncro.tech/aether/
• performance, tests, documentation

I.e. what is basic lens API? Not sure that interface ILens<T, P> is best or good one or enough for real world.

10 man days work to get it to be known:)

from imtools.

I wrote down the case when generic struct interfaces with unmanaged constrains and inlining via attribute and all possible in and ref with zero GC do work in C# and beat internal calls to CLR (C++ methods).

Also I tasks and tuples and other patters get double (class and struct semantics).

So should unions be structs and passed by ref? Should be 2 kinds of interfaces?

So yet another open question at least for me.

Another question how to pass equality compares. In immutable stuff comparing becomes more usable and more important. May be it is time in .NET for next design https://github.com/qbit86/misnomer#misnomerfictionary ?

from imtools.

Here is another experiment:
dotnet/corefxlab#2458

Funny thing, that this PR is close to approval to namespace Microsoft.Collections.Extensions.

from imtools.

Not now or maybe ImTools is not a good place for that.

from imtools.