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Fix primitive narrowing - #8993
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Nathan Shively-Sanders (sandersn) merged 2 commits intoJun 6, 2016
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| const enum Tag2 {} | ||
| declare function isNonBlank2(value: string) : value is (string & Tag2); |
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how is string & Tag2 structurally different from just string?
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Tag2 is a const enum (making the intersection nominal)
Nathan Shively-Sanders (sandersn)
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Jun 6, 2016
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👍 |
Nathan Shively-Sanders (sandersn)
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Jun 6, 2016
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I'll merge since Wesley's still waiting on commit privileges. |
ZpdDG4gta (zpdDG4gta8XKpMCd)
commented
Jun 7, 2016
is this approved by Anders Hejlsberg (@ahejlsberg), can i use it to build upon? |
Nathan Shively-Sanders (sandersn)
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Jun 7, 2016
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Yes, it turns out there's not much perf hit from this change. However, narrowing will not expand beyond this to methods. That's the performance cliff that Anders Hejlsberg (@ahejlsberg) was thinking of. |
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Fixes#7224.
Fixes#7441.
This is a re-submission of #7235 without the inversion of the type flag - meaning it simply adds all primitive types and intersection types to the narrowable types list.
Anders Hejlsberg (@ahejlsberg)Nathan Shively-Sanders (@sandersn)