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Optional local variables #41901
Description
Activity
But the variable in your example is not optional. It's always defined. You're confusing optional with "may be undefined".
Martin Johns (@MartinJohns) I am not confusing - that's exactly what I want. No matter how you name it, it would extend the already existing syntax and make it useful for local variables as well. You already can use it for class variables aka members/properties, so why not local as well
so why not local as well
It would complicate the implementation of #13195, if it ever is to be added. Optional properties and arguments can be missing, not only
undefined, which is a relevant difference.I don't think it makes sense to put the
?on the binding name; it's confusing. You wouldn't writelet array[]; the| undefinedis part of the type, not the variable. So the logical thing would benumber?, which we discussed to death when addingstrictNullChecks(since it might meannumber | null,number | undefined, ornumber | null | undefined) and decided to just not do since different people would rightly declare in a split plurality that it's "obvious" which one of those it should mean and be angry when 66% of them were surprised.Reacted by HansterI also support let name: string? to be equivalent to let name:string|undefined|null.
So as of current latest version, is this actually implemented?
Reacted by BribeI also support let name: string? to be equivalent to let name:string|undefined|null.
Including
nullwould just be plain confusing, because optional properties and parameters do not includenull.So as of current latest version, is this actually implemented?
No, and it (most likely) never will be implemented. The feature has been declined.
I also support let name: string? to be equivalent to let name:string|undefined|null.
Including
nullwould just be plain confusing, because optional properties and parameters do not includenull.So as of current latest version, is this actually implemented?
No, and it (most likely) never will be implemented. The feature has been declined.
Wonder why is this a bad thing, such that it is not implemented. verbosity can be greatly reduced if implemented. I mean if using question mark to represent undefined|null can cause confusion, then other characters can be considered.
Reacted by BribeReacted by Martin JohnsI think this is a great idea.
let result?: boolean;
It's obvious that
resultat this point isundefined. I don't think anyone in their right mind would think that it'snullfor example.Now, Martin Johns (@MartinJohns) argued that supporting this would complicate #13195 – meanwhile, on Jun 1, 2021 that issue was actually resolved.
Does this mean that in principle, TypeScript could support this syntax?
I totally agree with Anton Keks (@angryziber) on this:
let result: boolean | undefined = undefined // too verbose
And there's good code to be written that uses this syntax. In the example above, we can imagine that there is no result yet, neither success or failure.
Reacted by Caio Hamamura and Hanster
Suggestion
TypeScript already supports optional parameters and fields with a question mark.
Why not extend this feature to local variables as well, to allow them having an undefined value, e.g.
Use Cases/Examples
in this case specifying
numbertype is also optional:This would complete the usage of question mark
?as nullablity/unefineability operator, similar to Kotlin.Currently, defining an optional variable requires writing a lot of noise, e.g.
Checklist
My suggestion meets these guidelines: