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Apply type inference to mapObject[s.kind] #20190
Description
Activity
As a workaround, you can write
let printEntity2 = function <K extends Entity['kind']>(s: Entity & {kind: K}) { return areaFunctions[s.kind](s); };
There are multiple features that are not supported today that contribute to blocking this scenario.. first, The main is that a union property is not callable unless all variants have the same signature. so we would need #7294 first to be able to address this issue. Second we will need to distribute the union over the whole call expression, i,.e. the type of
areaFunctions[s.kind](s)would betypeof areaFunctions["named"](s) | tyoeof areaFunctions["decimal"](s) | | tyoeof areaFunctions["hex"](s); then we will need to do some narrowing onsin each branch based on the type ofs.kind.#7294 is the main issue, we currentlly have now way of resolving a union call.
Reacted by Aluan HaddadAutomatically closing this issue for housekeeping purposes. The issue labels indicate that it is unactionable at the moment or has already been addressed.
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on Jun 14, 2018
TypeScript Version: 2.6.1
Description
I am very impressed by the type inference TypeScript can do with
switchandfor...elsestatements.I miss, however, type inference for map object lookups.
Code
Expected behavior:
printEntity2 would compile
Actual behavior:
But it doesn't. I am forced to expand a single line into a long switch statement (just 3 lines here, but a lot more -- and often used -- in my project).