Re:TypeScript 5.2's New Keyword: 'using'
by radq on Monday June 19, 2023 @05:48AM
(#36389165)
I have some reservations about the specification - it looks like there are a lot of caveats to how it can be used. For example, it's allowed in for and for-of loops, but not in for-in loops. Also looks like destructuring will not be allowed.
[ Parent
| on HN ]
Considering this limitation, I wonder if the syntax could have been something else than assignment. Like maybe:
using getResource() as res;
Re:TypeScript 5.2's New Keyword: 'using'
by kybernetikos on Monday June 19, 2023 @06:24AM
(#36389404)
I agree. If it's assignment then it should work the same as assignment, otherwise it should have a different syntax.
Also seems like there would be use cases where you don't even want to assign the result, you just want the destructor to run at the end of the scope. Something like:
using someMutex.lock();
Re:TypeScript 5.2's New Keyword: 'using'
by carlhjerpe on Monday June 19, 2023 @10:55AM
(#36391775)
You assign it to a variable that is then disposed of once it's out of scope?
That's strange, what's the motivation behind not allowing destructuring? Seems very prudish.
It's ambiguous. Are you disposing of the object being destructured or the destructuring results? How do you make the distinction?
Much easier to not do it.
Not sure if this would produce more issues, but they could ignore c# and use something like:
const using x = getX()
const {using prop1, prop2} = using getX()
void using getX()
// x, prop1 and 2 anonymous Xs to dispose
To me it seems like disposing of the object being destructured is the natural solution. But I can see where others will disagree.
when would you want to do that?
When there’s a group of resources with a non-trivial disposal order but there’s no explicit manager object, for example.
Re:TypeScript 5.2's New Keyword: 'using'
by kuschkufan on Monday June 19, 2023 @08:07AM
(#36390102)
There is literally an example for using destructuring in the linked article. So it is supported.
Can you clarify where it indicates it's supported i.e. which specific example? I re read and didn't see it myself, seems others are missing it.
To be fair I don't see it not being supported either by the examples.
The last example:
{
await using { connection } = getConnection();
// Do stuff with connection
} // Automatically closed!
Thanks! Yes that example is subtly different.
I did also click through to the proposal but didn't see that issue. It does seem like it's still unclear what's intentional or not.
Re:TypeScript 5.2's New Keyword: 'using'
by pwdisswordfishc on Monday June 19, 2023 @02:40PM
(#36394953)
It’s intentional. The grammar production in the proposal is parametrized as ~Pattern (a parameter introduced in the proposal), which means it does not allow destructuring.
https://tc39.es/proposal-explicit-resource-management/#prod-...
> not in for-in loops
What would that even mean? The binding in a `for-in` can only ever hold a string, which can't be disposable. With a `for` or `for-of` the binding can hold an object, which is something you could dispose of.