Op 10-09-15 om 16:21 schreef Michael Torrie: > On 09/10/2015 01:27 AM, Antoon Pardon wrote: >> Op 09-09-15 om 19:55 schreef Steven D'Aprano: >>> In fairness to the C creators, I'm sure that nobody back in the early >>> seventies imagined that malware and security vulnerabilities would be as >>> widespread as they have become. But still, the fundamental decisions made >>> by C are lousy. Assignment is an expression? >> What is wrong with that? > Makes for a common error of putting an assignment in a conditional > expression like: > > if (a=4) this_is_always_true();
No it doesn't. You confuse a semantic characteristic with the specifix syntax that was chosen to express it in C. Should C have chosen '<-' as token for assignment, that error would have been far less common. The error is also facilitated because C doesn't have booleans and so everything can be used as one. If C would have had proper booleans and only allowed those as conditions in if and while statements, most of those errors would have been caught too, because the expression a=4 wouldn't produce a boolean. > GCC will give you a warning over that these days. But many C > programmers still adopt a notation of > > if (4 == a) do_something(); > > to protect them if they accidentally leave out one =. If assignment was > not an expression, then the compiler would properly error out every time > you used a solitary = in the conditional of an if statement. A language can provide this kind of protection and still allow assignment as an expression. A lousy syntactical choice, doesn't invalidate a particular choice in semantics. > Python strikes a good compromise. You can chain = in an assignment > statement, but you can't use them in a conditional expression. Python could have chosen other options, like a different assignment token, like providing a proper boolean type and expection such a type in a condition context. It could reverse the assignment so that you would have to write: expression = var, so that if someone accidently writes if var = expression instead of if var == expression, that would have been caught. It could combine some of these options. Now you possibly don't like these possibilities, but they show there are multiple syntactical possibilities that all allow for assignment as expressions, and that are less vulnerable than C for a specific kind of error. -- Antoon Pardon -- https://mail.python.org/mailman/listinfo/python-list
