On 27/11/20 12:11 am, Paul Sokolovsky wrote:
On Thu, 19 Nov 2020 18:53:01 +1300 Greg Ewing email@example.com wrote:
Note that this is *not* the same as introducing a new scope.
And that's very sad. That means instead of solving the root of the problem, adhoc workarounds are proliferated.
I'd be open to the idea of a variation on the for loop that does introduce a new scope for the loop variable. It would need new syntax, though.
I didn't suggest it initially because proposals for subscopes within functions typically meet with a lot of resistance, and I didn't want to get sidetracked arguing about that when it isn't strictly needed.
Million cells for million of iterations?
If your million iterations create a million nested functions that capture the variable and are all kept alive, then yes, you will get a million cells along with your million function objects.
If the loop doesn't have any nested functions, or they don't capture the loop variable, there will be 0 cells.
Note that the cells would still be needed even if there were a nested scope.
I'd suggest that it should be "for let"
That makes no sense as a phrase in English.
the scoping should be optimized to always treat "x" (as the "for" control variable) by-value,
That would make it very different from the way closures work anywhere else in the language.
for const x in some_iterator: ...
That will make it obvious that "x" is captured by value,
for const x in some_iterator: ... x = 1
Doesn't make sense (should lead to error - assigning to a const).
This is mixing up two different issues -- the scope of the loop variable, and whether it can be assigned to.
I proposed "new" because it directly gets at the important thing, which is that x is a *different* x each time round the loop.
So, there shouldn't be "special syntax". There should be generic syntax to solve Python's block scoping and const'ness issues.
Which people would then have to remember to use. By "special" in that context I mean "something you have to do differently to get your for loop to work the way you expect". Not necessarily something that can only be used with for loops.