On Friday, September 23, 2011 17:13 Walter Bright wrote: > On 9/23/2011 4:13 PM, Jonathan M Davis wrote: > > But while C++'s const is not as good as D's const, it's still very > > worthwhile IMHO. > > To me it's like buffer overflows. 99% of C/C++ code doesn't have buffer > overflows, and is perfectly reliable. But if someone hands you a 1,000,000 > line program and asks "ensure there are no buffer overflows" what are you > going to do? What are you going to do when Junior Programmer makes a patch > to your perfectly correct C/C++ code base, and now it has a subtle > overflow bug? Start all over with the review process? > > This is not an idle question, as a major focus of C static analysis tools > is to detect buffer overflows, and people spend a lot of effort & money on > them. > > Faith based programming works in the small, but programs grow ever larger > in size and complexity. Switching from faith to static guarantees is a > much more scalable technique. > > And where C++ const is really, really useless is when it comes to > multithreaded programming.
No, C++ does not give you an ironclad guarantee about correctness, and yes, it's absolutely useless for multi-threaded programming, but what it _does_ give you is still valuable. For instance, if I choose to use const_iterator instead of iterator, then when I screw up the call to <algorithm>'s copy function and mix up the iterators, the compiler will catch it and complain. When I try and call a non-const function on a const object, the compiler will complain. It will help me find errors in my code. And no, it won't help me find every const-related error, and no, there is no absolute guarantee that a const function _won't_ alter the object, but in general, it actually doesn't alter the object, and I have to specifically circumvent the compiler to be able to alter const stuff. Certain classes of bugs are caught because of const in C++. Even if the compiler can't take advantage of it for optimizations or whatnot, and even if it doesn't give as strong guarantees to the programmer as might be desirable, it _does_ help the programmer catch and prevent bugs. I completely agree with you that having static guarantees is better, but I don't think that the faith-based guarantees of C++'s const are worthless, just worse. - Jonathan M Davis