As a user, not implementer, I really want early errors. Perf costs of startup are negligible especially long-term. By the time ES6 is in browsers computers and phones should be faster by enough of a factor to mitigate any costs, whereas omitting early errors hurts developers indefinitely into the future.
On Sep 28, 2012, at 4:02, "Brendan Eich" <[email protected]> wrote: > Brendan Eich wrote: >> We have not discussed error-on-first-call in this thread at all! > > This needs a separate thread. The idea from last week's TC39 meeting was to > have not only > > * Early error, thrown before any code in the Program (grammar goal symbol) > containing the error, required by specific language in Clause 16. > > * Runtime error, all the other kinds. > > and now > > * Error on first call to a function, where the function contains what would > be an early error but for the supposed cost of early error analysis. > > The last case is really just a runtime error: a function with what should be > a static error becomes a booby trap: if your tests happen to miss calling it, > you'll feel ok, but a user who tickles the uncovered path will get a runtime > error. > > TC39 heard from some implementors who wanted to avoid more early error > requirements in ES6, or at least any that require analysis, e.g. reaching > definitions. > > That's fair as input to the committee, but implementation concerns are not > the only ones we weigh. And we were far from agreed on adding the "Error on > first call" category. > > The example you imply here would be > > function f(a, b = c, a = d) { > } > > and the duplicate formal a would be illegal because of the novel > default-parameter syntax. > > Making f into a proximity-fused bomb does not see either good or necessary. > The analysis requires to notice duplicate formals is trivial, and as I keep > pointing out, ES5 already requires it: > > function g(a, a) { > "use strict"; > } > > This must be an early error per ES5 clause 16. > > Given the ES5-strict sunk cost, there's no added implementation tax beyond > the logic conjoining duplicate detection with novel-syntax detection, which > is trivial. > > It'd be good to hear from Luke on this. > > /be > _______________________________________________ > es-discuss mailing list > [email protected] > https://mail.mozilla.org/listinfo/es-discuss > _______________________________________________ es-discuss mailing list [email protected] https://mail.mozilla.org/listinfo/es-discuss
