Add type-safe Ok.cast() and Err.cast() methods
#561
Merged
Conversation
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
When working with `Result`, users sometimes find it useful to cast the *other* case of the type. For example, given an `Ok<string, number>` (note: not a `Result<string, number>`), casting to `Ok<string, string>` is a safe no-op cast: we *know* we are in the `Ok` case, not the `Err` case, so the transformation is guaranteed to be legal. This is exactly equivalent to two other potential type representations, in fact: - `Ok<T> | Err<E>` - `Ok<T, never> | Err<never, E>` Implementing either of those types with the performance guarantees we currently have for True Myth *and* preserving type safety throughout is unfortunately not straightforward (or necessarily even possible), but `.cast()` allows us to get the benefits anyway.
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
When working with
Result, users sometimes find it useful to cast the other case of the type. For example, given anOk<string, number>(note: not aResult<string, number>), casting toOk<string, string>is a safe no-op cast: we know we are in theOkcase, not theErrcase, so the transformation is guaranteed to be legal. This is exactly equivalent to two other potential type representations, in fact:Ok<T> | Err<E>Ok<T, never> | Err<never, E>Implementing either of those types with the performance guarantees we currently have for True Myth and preserving type safety throughout is unfortunately not straightforward (or necessarily even possible), but
.cast()allows us to get the benefits anyway.