Warning on no constructor and super class constructor taking parameters #6979

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1. Ryan Cavanaugh (RyanCavanaugh)

   added

   By DesignDeprecated - use "Working as Intended" or "Design Limitation" insteadDeprecated - use "Working as Intended" or "Design Limitation" instead

   on Feb 9, 2016
2. RyanCavanaugh commented on Feb 9, 2016

   

   Ryan Cavanaugh (RyanCavanaugh)

   on Feb 9, 2016

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   Note that you can't just write

   let x = new Child();

   And that the generated code calls super for you:

   var Child = (function (_super) {
       __extends(Child, _super);
       function Child() {
           _super.apply(this, arguments); <---
       }
       return Child;
   })(Parent);

   Based on reading the linked issue, it sounds like you're depending on a DI framework that reflects over the code to figure out what parameters to pass a constructor. In this case, it's up to you to reflect that behavior in your class one way or another (is static $inject = [...] available to you?).

   After shipping for three years with the desirable behavior of "Derived classes with no declared constructors automatically get their base class's constructors", it's not feasible to break everyone and tell them to go manually rewrite their constructors so that users of particular DI frameworks get better warnings in some cases.

   It would be very easy to write a no-implicit-constructors TSLint rule if that's the kind of thing you wanted to enforce in your project.
3. Ryan Cavanaugh (RyanCavanaugh)

   closed this as completedon Feb 9, 2016
4. staeke commented on Feb 9, 2016

   

   Staffan Eketorp (staeke)

   on Feb 9, 2016

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   Sorry....my bad. This didn't make sense at all. Of course it shouldn't. Full story:

   This comes from an Angular 2 use case. The Parent has some decorators for dependency injection. These aren't picked up by Angular since they aren't exposed by Child. The (ES5) javascript generated is

   _super.apply(this, arguments)
   

   ...which works fine invocation wise, but not decoration wise.
5. staeke commented on Feb 9, 2016

   

   Staffan Eketorp (staeke)

   on Feb 9, 2016

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   Ryan Cavanaugh (@RyanCavanaugh) you're so right! Well guessed!
6. staeke commented on Feb 9, 2016

   

   Staffan Eketorp (staeke)

   on Feb 9, 2016

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   Ryan Cavanaugh (@RyanCavanaugh) I think a better question would be: can we open up for Angular (and similar) to deduce in runtime the constructor hierarchy and look for decoration metadata in the parent. This currently seems impossible (unless I'm mistaken)
7. microsoft

   locked and limited conversation to collaborators on Jun 19, 2018