[stdlib] Align behavior of generic NaN conversion to that of concrete types #17746
Conversation
This file contains hidden or 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
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Outdated suggestions cannot be applied.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.
Double.init(exactly: Float)checks that the converted value is "exact" by checking for equality. Therefore, NaN is never "exactly" converted.Whether NaN should always or never be considered "exactly" NaN for the purposes of conversion has been discussed at some length. As @stephentyrone puts it, "Either behavior is weird to some people, but the current behavior is easier to explain: the initializer succeeds if the round-tripped value compares equal."
In #13782, I implemented generic floating-point conversion of NaN; that method checks for exactness by looking at the payload, which is inconsistent with the behavior of its concrete counterparts. This PR aligns the behavior for consistency.