Expose .is() typeguard on SharedObjectKind

[Abe27342]

Description

With the removal of concrete DDS classes, one pattern that's come up repeatedly is customer code which previously checked instanceof MySharedObject (usually when the code supported multiple shared object types for whatever reason), which no longer works. This change adds a drop-in replacement to the public API surface.

Breaking Changes

As SharedObjectKind was marked sealed, this is non-breaking.

Alternatives Considered

We could expose free functions in each package easily e.g. by using a helper like this:

export function createSharedObjectTypeguard<TSharedObject>(
	kind: ISharedObjectKind<TSharedObject>,
): (loadable: IFluidLoadable) => loadable is IFluidLoadable & TSharedObject {
	const factoryType = kind.getFactory().type;
	return (loadable: IFluidLoadable): loadable is IFluidLoadable & TSharedObject => {
		return isChannel(loadable) && loadable.attributes.type === factoryType;
	};
}

Ultimately this will be more code though and arguably less discoverable.

We could also add back support for instanceof using Symbol.hasInstance (and the same implementation as .is), but due to microsoft/TypeScript#56536, this won't work for customers using TS below 5.5, so we'll need something else anyway at least for now.

[anthony-murphy]

I like this. Its discoverable, and an easy change given that all instanceof uses already have the shared object type. curious how @CraigMacomber feels about having an implementation leak through the type erasure like this, and if he foresees any problems from that

[msfluid-bot]

⯅ @fluid-example/bundle-size-tests: +708 Bytes

Metric Name	Baseline Size	Compare Size	Size Diff
aqueduct.js	457.54 KB	457.63 KB	⯅ +91 Bytes
azureClient.js	555.3 KB	555.41 KB	⯅ +116 Bytes
connectionState.js	680 Bytes	680 Bytes	■ No change
containerRuntime.js	258.68 KB	258.7 KB	⯅ +14 Bytes
fluidFramework.js	391.52 KB	391.58 KB	⯅ +70 Bytes
loader.js	134.07 KB	134.08 KB	⯅ +14 Bytes
map.js	42.12 KB	42.18 KB	⯅ +64 Bytes
matrix.js	145.63 KB	145.69 KB	⯅ +64 Bytes
odspClient.js	523.08 KB	523.18 KB	⯅ +105 Bytes
odspDriver.js	97.17 KB	97.19 KB	⯅ +21 Bytes
odspPrefetchSnapshot.js	42.27 KB	42.29 KB	⯅ +14 Bytes
sharedString.js	162.64 KB	162.7 KB	⯅ +64 Bytes
sharedTree.js	382.03 KB	382.09 KB	⯅ +64 Bytes
Total Size	3.27 MB	3.27 MB	⯅ +708 Bytes

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Baseline commit: 957b194

Generated by 🚫 dangerJS against 4c97f7c

[CraigMacomber]

I like this. Its discoverable, and an easy change given that all instanceof uses already have the shared object type. curious how @CraigMacomber feels about having an implementation leak through the type erasure like this, and if he foresees any problems from that

I don't think this is leaking any implementation info: nothing in the exposed API says how it works (well the remarks comment does a bit, but I think thats ok as its documenting historical things not usage contracts)

One of the reasons I created SharedObjectKind was to be able to add things like this to all of them in a consistent way easily. Since the interface is sealed, we are allowed to add to it like this as a non breaking change.

I don't see any problem supporting this going forward. either, so I think its a good change.