968214 - Feature: try / success

Status: RESOLVED INVALID

(Core :: JavaScript Engine, defect)

Description

[David Teller [:Yoric] - still alive but not very active]

Consider the following pattern:

let foo;
try {
  foo = f();
} catch (ex1 if ...) {
  // ...
} catch (ex2 if ...) {
  // ...
} finally {
  close();
}

// Now do something with foo

With an appropriate keyword "success", we could rewrite something almost equivalent as:

try {
  f();
} success (foo) {
  // Now do something with foo
} catch (ex1 if ...) {
  // ...
} catch (ex2 if ...) {
  // ...
} finally {
  close();
}

This would put the "Now do something with foo" closer to f(), and keep error-handling on the outside, which I believe is more readable.

Comment 1

[Boris Zbarsky [:bzbarsky]]

So this differs from this:

try {
  let foo = f();
  // Now do something with foo
} catch (ex1 if ...) {
  // ...
} catch (ex2 if ...) {
  // ...
} finally {
  close();
}

in that it calls close() before doing the "something" (which would be a bit weird, in the success() setup) and doesn't catch exceptions from the "something"?

Comment 2

[David Teller [:Yoric] - still alive but not very active]

Exactly.

Comment 3

[Jason Orendorff [:jorendorff]]

I've occasionally wanted something like this. However, as long as TC39 is chugging along, our JS engine is not taking new language features that aren't standard-track.

Propose it on es-discuss or (better still) talk it over with one of Mozilla's TC39 representatives (Dave Herman, Allen Wirfs-Brock, or Brendan Eich).

I think the part of this that might give them pause will be the use of the block `{ f(); }` as an expression producing a value. What if it's an if-statement in there? and so on.