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Merge pull request #85 from swan-io/expiriment-referential-equality
Experiment: referential equality
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,63 @@ | ||
| const weakRefFallbackMap = new WeakMap(); | ||
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| interface WeakRefLike<T extends WeakKey> { | ||
| deref(): T | undefined; | ||
| } | ||
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| // We can replicate the WeakRef for older browsers using a `WeakMap` using | ||
| // the weakref-like instace as key. | ||
| const WeakRefWithLegacyFallback = | ||
| typeof WeakRef === "function" | ||
| ? WeakRef | ||
| : class WeakRefWithFallback { | ||
| constructor(value: unknown) { | ||
| weakRefFallbackMap.set(this, value); | ||
| } | ||
| deref() { | ||
| return weakRefFallbackMap.get(this); | ||
| } | ||
| }; | ||
| // For each tag variant that can contain a value (`Some`, `Ok`, `Error`, `Done`), we create a store. | ||
| // The store enables us to keep a map of `value` to the container of this `value`. | ||
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| // The container is stored through a `WeakRef`, ensuring that we don't prevent the containers | ||
| // from being garbage-collected. | ||
| export const createStore = () => { | ||
| const store = new Map<unknown, WeakRefLike<object>>(); | ||
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| // We subscribe to the garbage collection, to make sure we don't keep in memory | ||
| // some values that we don't need as keys, because if all instances of a container of | ||
| // a given value have been garbage collected, there isn't any comparison required. | ||
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| // For instance, let's say we have an object `x`, and create a `Option.Some(x)`: | ||
| // 1. As long as `Option.Some(x)` isn't garbage collected, | ||
| // it means that the value needs to remain stable as it can be compared to | ||
| // another `Option.Some(x)`. | ||
| // 2. If all references to `Option.Some(x)` are garbage collected, it means that | ||
| // it's safe to dispose, as we don't have anymore requirement for comparison. | ||
| // 3. If we re-create an `Option.Some(x)` afterwards, the first one re-created is | ||
| // the new basis for comparison. | ||
| const registry = | ||
| typeof FinalizationRegistry === "function" | ||
| ? new FinalizationRegistry((value) => { | ||
| store.delete(value); | ||
| }) | ||
| : undefined; | ||
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| return { | ||
| set: (key: unknown, value: object) => { | ||
| store.set(key, new WeakRefWithLegacyFallback(value)); | ||
| // Older browsers that don't have `FinalizationRegistry` don't benefit | ||
| // from the memory cleanup, but that's fine as a best-effort thing | ||
| if (registry !== undefined) { | ||
| registry.register(value, key); | ||
| } | ||
| }, | ||
| get: (key: unknown): unknown => { | ||
| const value = store.get(key); | ||
| if (value !== undefined) { | ||
| return value.deref(); | ||
| } | ||
| }, | ||
| }; | ||
| }; |
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