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Re: math.abs(math.mininteger) (Was: Must "attempt to get length of a number value" be an error?

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On 14/05/2019 21:41, Will Crowder wrote:

On Mon, 2019年05月13日 at 09:49 +0200, Lorenzo Donati wrote:
[snip]

I'm not a big fan of C (and C++ either: C++ it has almost the same
definition of UB as C), but I had to reconsider my views in the last 5
years, since I had to cope with microcontroller (MCU) software development.
I agree that, in an ideal world, no sane high level application should
be developed in C (or C++) because they are intrinsically unsafe, thanks
to UB. C++ mitigates that a little by providing high level constructs
that a programmer can use to avoid the most common cases where a mistake
can cause UB (e.g. dynamic memory management).

C in the right hands (e.g., folks who understand language standards and
how to avoid or allow for undefined behavior) is incredibly useful for
high level applications, especially where performance is an issue. It's
a matter of understanding the tools you're using.

Sorry, but I don't exactly get the point you are trying to make.
"C in the right hands...is incredibly useful for high level applications, especially where performance is an issue." OK, so what? How this contradicts the fact that literature (technical, academic, etc.) is full of cases where C lacks of "safety checks" ends up biting the programmer and the user with vulnerabilities? Developers aren't perfect. Training a programmer to have the same productivity in C with the same rate of "bug introduction" as another, more constrained language, is extremely costly. "In the right hands" even assembly can be used to do high level applications. This doesn't mean that assembly is a good choice for that. I stand by my opinion that C is not meant to be a safe language and pure speed is the need of only an handful of application areas (where C can be used effectively). If C were the magic tool that "in the right hands" would solve all the programming problems, there wouldn't have been decades of development in new, safer, languages. C, IMO, is not /the/ right tool for /any/ job. Is the right tool for /some/ very specific jobs. In other cases C is just the only available alternative to assembly, so it turns out to be immensely better, but only for lack of a better alternative. And as an example of the fact that C is insane in some of its aspect, consider this: namespacing. What kind of sane modern language would require programmers to remember that: 
1. any identifier beginning with "str" are reserved,
2. any identifier beginning with "mem" are reserved,
3. any identifier defined in any included header are reserved,
4. etc.
If you redefine such identifier you trigger UB!!!
So I, as a C programmer, I must know EVERY SINGLE ONE identifier defined in <stdio.h>, but... no! if <stdio.h> includes other headers, I must know any other identifier defined in them. So I either know the inclusion tree of any library header or I "simply" remember every identifier defined in the whole library!!! That's an enormous effort for a developer's memory, which is plainly silly, and it is justifiable only because modern C is backward compatible with it C89 standard, which is somewhat compatible with that old thing K&R devised in the late 60s!!! It's a relic of the past. Its limitations were justifiable in the 80s, when SW engineering was in its infancy and computers with MBs of RAM were a dream. Nowadays is plainly silly. It's only the economics behind the huge C codebase that prevents people designing and/or using other, better /system/ languages. The very fact that C++ has found fertile ground is a proof that C is not the silver bullet. Although C++ retains all the risks of C (by design), its higher level features allows it to build powerful abstractions that can be used to shield the programmer from most causes of UB (e.g. RAII techniques, OO support, templates, a extremely rich library with lots of data structures that avoid the user direct memory management, and decent namespacing!, etc.). Again, as I said, I had to reconsider my extremely critic view on C in the latest years. It has its advantages even today: it is as universal as you can get for a computer language, and it is simple enough to be learned easily. If you are careful and you don't try to be too smart, you can avoid many pitfalls. But still, you always pay for something you don't need or use: if you don't need ultra-optimized code and max speed, or access to the bare metal, you still must be extra wary for even the innocuous looking (1 << 16) expression (that's UB on implementations where ints are 16 bit wide!!!). 
And in fact, many of
the "higher" level languages have implementations written in C. Does
that mean it would be "insane" to code a "high level application" in any
language whose underlying implementation was written in C? I'd think
not.
How the fact that an higher level language implementation may be written in C does render the higher level language intrinsically unsafe as the underlying C? If the language is implemented correctly, and it is meant to be safer than C, the compiler/interpreter programmer will have coded checks and systems that shields the end-user (the would-be programmer of the higher level language) from the underlying C problems. I never said that you can't write a safe application in C (but it is very difficult, with all the loopholes). I said that C is unsafe as it is specified: you have to provide all the possible checks to make the application safe. This is a huge amount of work for most applications. A simple integer overflow is UB in C. And that's not because it can't be made well-defined, but because that would thwart optimizations opportunities on some platforms (even if it is NOT your platform!), just for the sake of portability. Should any application programmer worry about any innocent-looking integer expression he writes because it could trigger UB in some obscure corner case? That's insane, I repeat it, for most applications. "Fail fast and fail loudly". That's one of my favorite SW engineering mottos. UB is utterly unpredictable. Change compiler version down the road and some code that has worked for ages now is broken just for a silly bug that could have been spotted from the beginning, had the language be, for example, Lua. 
Will

Cheers!
-- Lorenzo

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