Type Inference does not work for generics with default types #19205

Activity

1. mhegazy commented on Oct 16, 2017

   

   Mohamed Hegazy (mhegazy)

   on Oct 16, 2017

   Contributor

   More actions

   Currently generic type inference happens only when no generic type arguments are provided. specifying at least one disables all generic inference.
   #10571 tracks allowing partial generic inference for required parameters. I would say we will do the default automatic inference in the same change.
2. mhegazy commented on Oct 16, 2017

   

   Mohamed Hegazy (mhegazy)

   on Oct 16, 2017

   Contributor

   More actions

   closing in favor of #10571
3. Mohamed Hegazy (mhegazy)

   added

   DuplicateAn existing issue was already createdAn existing issue was already created

   on Oct 16, 2017
4. jpkraemer commented on Oct 17, 2017

   

   Jan-Peter Krämer (jpkraemer)

   on Oct 17, 2017

   Last edited by jpkraemer

   Author

   More actions

   Thanks for the clarification, indeed the following example works:

   function test<T, R>(param: FormattedDataProvider<T, R>) {
     console.log(param); 
   }
   
   test({
     src: { a: 23 },
     format: v => String(v.a)
   })

   This one however, does not. So even when not specifying any types, the defaults might disable inference, too, in some instances.

   type FormattedDataProvider<T, R = {}> = {
     src: R,
     format: (item: R) => T
   }
   
   type UnformattedDataProvider<T> = {
     src: T
   }
   
   type ConfiguredDataProvider<T> = FormattedDataProvider<T> | UnformattedDataProvider<T>;
   
   function test<T>(param: ConfiguredDataProvider<T>) {
     console.log(param); 
   }
   
   test({
     src: { a: 23 },
     format: v => String(v.a)
   })
5. mhegazy commented on Oct 17, 2017

   

   Mohamed Hegazy (mhegazy)

   on Oct 17, 2017

   Contributor

   More actions

   in the above example, you have used FormattedDataProvider<T> in the definition of ConfiguredDataProvider<T> without a second argument. this is identical to FormattedDataProvider<T , {}>.

   if you wanted to propagate the optionality of the second argument you would write it as:

   type FormattedDataProvider<T, R = {}> = {
       src: R,
       format: (item: R) => T
   }
   
   type UnformattedDataProvider<T> = {
       src: T
   }
   
   type ConfiguredDataProvider<T, R = {}> = FormattedDataProvider<T, R> | UnformattedDataProvider<T>;
   
   function test<T, R = {}>(param: ConfiguredDataProvider<T, R>) {
       console.log(param);
   }
6. mhegazy commented on Oct 31, 2017

   

   Mohamed Hegazy (mhegazy)

   on Oct 31, 2017

   Contributor

   More actions

   Automatically closing this issue for housekeeping purposes. The issue labels indicate that it is unactionable at the moment or has already been addressed.
7. Mohamed Hegazy (mhegazy)

   closed this as completedon Oct 31, 2017
8. microsoft

   locked and limited conversation to collaborators on Jun 14, 2018