On Mon, Sep 28, 2015 at 1:00 PM, Carl Meyer <carl@oddbird.net> wrote:
On Mon, Sep 28, 2015 at 12:43 PM, Carl Meyer <carl@oddbird.net Or put differently, that whereas these two are trivially equivalent (the definition of left-to-right binding within a precedence class):
foo.bar.baz (foo.bar).baz
these two are not equivalent:
foo?.bar.baz (foo?.bar).baz
Right.
I'm having trouble coming up with a parallel example where the existing short-circuit operators break "extractibility" of a sub-expression
On 09/28/2015 01:53 PM, Guido van Rossum wrote: like
that.
Why is that an interesting property?
Because breaking up an overly-complex expression into smaller expressions by means of extracting sub-expressions into temporary variables is a common programming task (in my experience anyway -- especially when trying to decipher some long-gone programmer's overly-complex code), and it's usually one that can be handled pretty mechanically according to precedence rules, without having to consider that some operators might have action-at-a-distance beyond their precedence.
Well, if just the foo?.bar.baz part is already too complex you probably need to reconsider your career. :-) Seriously, when breaking things into smaller parts you *have* to understand the shortcut properties. You can't break "foo() or bar()" into a = foo() b = bar() return a or b either.
I guess this is because the proposed short-circuiting still "breaks
out
of the precedence order" in a way that the existing short-circuiting operators don't. Both member access and indexing are within the same left-to-right binding precedence class, but the new operators would
have
a short-circuit effect that swallows operations beyond where normal left-to-right binding would suggest their effect should reach.
Are there existing examples of behavior like this in Python that I'm missing?
I don't know, but I think you shouldn't worry about this.
I think it's kind of odd, but if nobody else is worried about it, I won't worry about it either :-)
Good idea. -- --Guido van Rossum (python.org/~guido)