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Override keyword should not be required on optional base type members, without implementations. #44439
Description
Bug Report
🔎 Search Terms
override keyword optional
🕗 Version & Regression Information
- This is new functionailty released in 4.3.0
⏯ Playground Link
Playground link with relevant code
💻 Code
abstract class BaseType {
abstract requiredSettings(): object;
customInit?(): Promise<void>;
}
class Specialization extends BaseType {
requiredSettings() {
return {};
}
async customInit() {
// .. do something
}
}🙁 Actual behavior
When using the noImplicitOverride flag, an optional base type field, with no implementation, requires the override keyword. By contrast abstract methods do not require the override keyword.
🙂 Expected behavior
An optional field, with no implementation in the base class should not require the override keyword.
Activity
[-]Override keyword behavior and optional base type members.[/-][+]Override keyword should not be required on optional base type members, without implementations.[/+]RyanCavanaugh commentedon Jun 7, 2021
(Crossposting this comment) This is intentional. The mental model to have in place here is, "If I typo this method name, what will happen?"
If you typo the name of an abstract member (assuming you're in a concrete class), you'll get an error, because you failed to implement all abstract members.
overrideisn't necessary to prevent you from making this mistake, so you don't need to writeoverridein this case.If you typo the name of an optional member, you'll now have
calculateHeightandcacluateHeight, and the latter will just go silently uncalled forever.overrideis necessary to prevent you from making this mistake, so when overriding an optional member, you should be writingoverride.arciisine commentedon Jun 7, 2021
Ryan Cavanaugh (@RyanCavanaugh) thanks for the reply. I definitely understand the design goal of explicit declaration here. The challenge I'm seeing is the mismatch between class members that are optional, and interface methods that are optional. It appears interfaces are not held to the same standard as classes, and abstract class members are treated differently than non-abstract.
Below will actually throw a compilation error, as override is not supported on interface methods. I'm not sure if this is a gap, but it seems inconsistent from the perspective of abstract classes and interfaces achieving similar goals.
RyanCavanaugh commentedon Jun 7, 2021
It's intentional that
overridedoesn't apply toimplementsclauses, since you're not overriding anything.arciisine commentedon Jun 8, 2021
Right, but I'd argue that an optional member on an abstract class is not being overridden either, since it does not have an implementation. The scenario you provided with
calculateHeightandcacluateHeight, should apply equally to an interface as much as it does to a base class, in terms of risk to incorrectly honoring the contract:vs
arciisine commentedon Jun 8, 2021
Ryan Cavanaugh (@RyanCavanaugh) From conversation it appears the goal of
overrideis to support explicit declaration of specialized class implementation, excluding abstract methods. This is with the express goal to ensure that if the parent class modifies the function declaration, that the child class will fail compilation if it no longer honors the contract.I still believe this desire/need can apply to interfaces as well, though the current issue has a work around. By declaring the optional method via an interface, the compiler will no longer consider the method a candidate for overriding, and so will not complain. It feels a little clunky, especially given abstract classes cannot implement interfaces with optional members.
typescript-bot commentedon Jun 10, 2021
This issue has been marked 'Working as Intended' and has seen no recent activity. It has been automatically closed for house-keeping purposes.