On Fri, 12 Aug 2016 07:38 pm, BartC wrote: > 'year' has been spelled wrongly
How do you know? The point is that it is intentional that callers can set arbitrary attributes on (most) objects. It is perfectly legitimate to set: d.year d.century d.owner d.extra_seconds and, yes, even d.yaer, since it isn't the compiler's job to check your spelling or critique your choice of variable names. If you want to spell check your code, run a spellchecker[1], or a linter, or have a human review it. Or all three. There are broadly two tactics that a language can take when it comes to attribute (or more widely, variable) names: (1) Editing is cheap, but compiling and testing code is expensive, and the consequences of accessing a non-existent variable are catastrophic (overwriting arbitrary memory, accessing uninitialised memory, segmentation faults, execution of arbitrary code, security vulnerabilities, etc). Therefore it is important that the compiler check ahead of time that every name referenced exists and has been declared. (2) Compiling and testing code is cheap, and the consequences of accessing non-existent variables are mild. Since typos are generally rare (say, one name out of a hundred is mispelled), requiring declarations is a waste of effort. Rare errors will be caught through human review, linters, and testing. The first time I ever compiled a full-sized application (not a particular large one either, it was a text editor a little more featureful than Notepad) it took something like nine hours to compile on a Mac SE (this was circa 1990). How mad would I have been if, eight hours and thirty minutes into the compilation, the compiler suddenly stopped with an error caused by a mistyped variable name? Today, I could probably compile the equivalent program in a minute. Do I care if the compiler doesn't pick up the typo until 58 seconds through the process? Not a whit. I would care if the compiler doesn't pick up the error *at all* and I'm writing in a low level language where accessing a non-existent variable allows Bulgarian hackers to steal the money in my bank account, so there's still some advantage to having declarations in low-level languages. It *absolutely makes sense* to require variable declarations (possibly including type information, where it cannot be inferred) when the consequences of a typo are routinely expected to be severe. Under those circumstances, a "bondage and discipline" language that forces you to be absolutely pedantic to satisfy the compiler can be a good thing. Turn it around though: one of the reasons why languages like Ruby, Javascript, Lua, Python, Perl etc are so ridiculously productive is that you don't have to keep stopping to declare variables just to satisfy the compiler. Need a new variable? Just assign to it and keep going -- there's no, or very little, mental task switching. Another reason why such languages are so productive is the availability of an interactive REPL where you can try out code interactively. How clumsy and awkward the REPL would be if you had to keep declaring variables ahead of time. The cost of that flexibility is that I have to pay a little bit more attention when doing a code review, I have to write a few more tests. But the edit-compile-run cycle is so ridiculously fast that this doesn't really matter. Programmers have invented entirely new coding paradigms, Test Driven Development and Agile, to take advantage of this speed and flexibility. Sure, you can take TDD and Agile into the realm of statically typed languages, but it will always be like running a sprint wearing a suit of armour. You can do it, but you'll be out-paced by the sprinter wearing track shoes and Lycra. [1] Are there programming language aware spell checkers? If not, there should be. -- Steve “Cheer up,” they said, “things could be worse.” So I cheered up, and sure enough, things got worse. -- https://mail.python.org/mailman/listinfo/python-list
