Stricter type definition of Subject #5307
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6 tasks
cartant
reviewed
Feb 10, 2020
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@cartant I added tests and some documentation to explain the breaking change and the motivation for choosing |
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Nevermind, this is only a breaking change for TS 2.x and lower, which we would be breaking for people in v7 anyhow. |
benlesh
approved these changes
Apr 3, 2020
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Description:
Make type definition of
Subjectmore strict to avoid common bugs when using Subject.Related issue (if exists):
This issue been discussed extensively in #2852 and #5066 .
Sensitive points
As discussed in the issues linked above, it is possible to omit the argument to
nextwhen the Subject is of typeSubject<void>.When the template type is anything other than
void, then an argument fornextis required.The primary case where this can be a problem is when people instantiate
Subject<any>and then usesubject.next()with no arguments. This will break.The present change makes the default template type of Subject
voidinstead ofany. This means that when you writenew Subject(), you get aSubject<void>(instead ofSubject<any>) and are therefore able to writesubject.next()orsubject.next(value)ifvalueis eitheranyorundefined.Other good candidates for default template type are
unknownandany. We can discuss whethervoidis the best choice here, I am not completely sure yet.