Suggestion Backlog Slog, 9/13/2017 #18394

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1. Ryan Cavanaugh (RyanCavanaugh)

   added

   Design NotesNotes from our design meetingsNotes from our design meetings

   on Sep 11, 2017
2. RyanCavanaugh commented on Sep 18, 2017

   

   Ryan Cavanaugh (RyanCavanaugh)

   on Sep 18, 2017

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   • Surprising Not all code paths return a value #18319 Perhaps-unexpected implicit return error is bad?
     • Consistency of contextual return type vs predictability of when this should happen
     • 👍
   • allow typeof expressions in extends and implements list #18271 Allow typeof in extends / implements clauses
     • For extends this is bad
     • For implements this is doable with parser changes
     • Concerns about parsing
     • 👎 Write a type alias
   • Cannot implement generic type guarding function #18202 Make type guards be an inference position
     • 👍
   • Merging constants with namespaces #18163 Merge value namespaces with other values
     • We can't emit the var statement in this case
     • Does this merge with the variable or the type?
       • The variable: Now the declared type isn't the actual type?
       • The type: Now you're changing random other types, maybe accidently?
     • 👎 Demonstrate how to type this library using existing mechanisms
   • Discriminated Unions don't cast with single type #18056 Single-case discriminated unions don't produce never
     • Now we'd be doing CFA for all types? Or just those containing unit types?
       • Currently CFA only applies to union types
     • Workaround is good enough
     • 👎
   • Need way to express hybrid types that are indexable for a subset of properties  #17867 "Fallback" index signatures for non-declared properties only
     • You can use intersection types to work around this behavior
       • Except not really
     • [...]: string ?
     • AMF, esp. use cases from DT
   • Star-imported module should conform to the type of a string-indexed object #17622 Module object imports should be able to implicitly satisfy index signatures
     • 👍 check if the originating symbol for the declared type is an import *; or try setting the same flag on import *s as object literals
   • Extending string-based enums #17592 Extending an existing string enum
     • Dan's wanted it forever
     • Currently these types are distinct and the derived type will not be compatible with the base type
     • Nice idea but not a big demand for it yet
     • Some pretty good workarounds exist
     • AMF
   • Infer extra parameter types from default values #17559 Issue an implicit any warning on an implicit-any parameter
     • Every falseandtru bug starts with a riddle :laugh:
     • How did this code get written...?
     • 👍 Try not providing a contextual type if the arity count is wrong
   • SUGGESTION: enable forceConsistentCasingInFileNames by default #17542 Turn on consistent filename enforcement by default
     • Breaking change that annoys Windows people
       • But random breaks from this being off are breaking tools even on Windows
     • This is the Right Thing to Do (tm)
     • Wailing and gnashing of teeth from VS users
     • Rathole on tsc --init
     • 👍 👎 on for tsc --init but off by default
   • Add simulated nominal type for COM SAFEARRAY and VarDate to lib.scripthost.d.ts #17526 Add psuedonominal type for VarDate and COM SAFEARRAY in lib.scripthost.d.ts
     • 👍 Accepting PRs
   • Recursive generics in function parameters are inferred as {}, and produce funky Intellisense #17522 Recursive generic constraint produce unexpected {}
     • Super unclear how we would get this to work
   • Support inferred string-modified union types #17512 Support inferring types of concatenation of string constants/unions
     • Concern about combinatorial explosion of types
     • Without a way to quickly declare the output types, there's not much use
   • Suggestion: CFA, assignment, strict null checks and function scope #17449 Better CFA when a variable is definitely initialized (and stays initialized)
     • We don't have the extra pass necessary to detect that there are no further assignments
     • Use const per usual
     • Deferred until there would be a more positive set of outcomes from adding an additional pass
   • Typescript forbids safety checks that check equality of values with different generic types #17445 Allow comparison of any two type variables
     • Sound, but wat
       • Technically any === operation is sound but that doesn't make it a good idea
     • 👎

   Bonus slog: How to ban [1, 2, 3].sort() ?
3. Ryan Cavanaugh (RyanCavanaugh)

   closed this as completedon Feb 5, 2018
4. microsoft

   locked and limited conversation to collaborators on Jul 3, 2018