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RegExpMatchArray has lost some compatibility with Array since 2.1.0-dev.20160729 #10041

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RegExpMatchArray has lost some compatibility with Array since 2.1.0-dev.20160729#10041
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ahejlsberg
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BugA bug in TypeScriptFixedA PR has been merged for this issue
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TypeScript 2.0.2

Description

@falsandtru
falsandtru (falsandtru)
opened on Jul 30, 2016

TypeScript Version: master

Code

(''.match(/ /) || []).map(s => s.toLowerCase());

Expected behavior:

$ node built/local/tsc.js --lib es6 --strictNullChecks index.ts

Actual behavior:

$ node built/local/tsc.js --lib es6 --strictNullChecks index.ts
index.ts(1,1): error TS2349: Cannot invoke an expression whose type lacks a call signature.

Activity

  1. RyanCavanaugh commented on Jul 30, 2016

    @RyanCavanaugh
    Ryan Cavanaugh (RyanCavanaugh)
    on Jul 30, 2016
    Member

    Same root cause as #10025 but it's much less clear how to fix this example

  2. falsandtru commented on Jul 30, 2016

    @falsandtru
    falsandtru (falsandtru)
    on Jul 30, 2016
    ContributorAuthor

    I understand as a breaking change, not a bug. Thanks Ryan Cavanaugh (@RyanCavanaugh) .

  3. ahejlsberg commented on Jul 30, 2016

    @ahejlsberg
    Anders Hejlsberg (ahejlsberg)
    on Jul 30, 2016
    Member

    Several subtle issues at play here. With #9407 we still perform subtype reduction for the operands of the || and ?: operators. However, even after subtype reduction the expression (''.match(/ /) || []) has type RegExpMatchArray | never[] because there are extra optional properties introduced by RegExpMatchArray. In the property access for the map property we would previously perform subtype reduction again, and that would reduce the union function type of map down to a single type. This step we now omit because of #9407.

    I think the real issue here is that we produce the union type RegExpMatchArray | [] instead of just RegExpMatchArray (and this issue was there all along). It may be that for || and ?: we should say that if neither operand is a subtype of the other, but one is assignable to the other, we pick the type of the one to which the other is assignable.

  4. Anders Hejlsberg (ahejlsberg)
    reopened this on Jul 30, 2016
  5. Anders Hejlsberg (ahejlsberg)
    added
    BugA bug in TypeScript
    on Jul 30, 2016

  6. falsandtru commented on Jul 30, 2016

    @falsandtru
    falsandtru (falsandtru)
    on Jul 30, 2016
    ContributorAuthor

    Thanks for the fix!

  7. Ryan Cavanaugh (RyanCavanaugh)
    added this to the milestone on Aug 1, 2016
  8. Ryan Cavanaugh (RyanCavanaugh)
    assigned
    Anders Hejlsberg (ahejlsberg)
    on Aug 1, 2016
  9. Anders Hejlsberg (ahejlsberg)
    closed this as completedin #10069on Aug 1, 2016
  10. Anders Hejlsberg (ahejlsberg)
    added
    FixedA PR has been merged for this issue
    on Aug 1, 2016
  11. microsoft
    locked and limited conversation to collaborators on Jun 19, 2018
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