> You can't use them for safety checks, because you must assume they won't be run.
This is also true of assert, though. It can be compiled out so shouldn't be used for anything that must run.
This is also true of assert, though. It can be compiled out so shouldn't be used for anything that must run.
That's the opposite of what NDEBUG does. https://en.cppreference.com/cpp/error/assert
Critical bit:
> 1) If NDEBUG is defined as a macro name at the point in the source code where <cassert> or <assert.h> is included, the assertion is disabled: assert does nothing.
It also is impossible to guarantee it unless you're the only one compiling the program. If you've built a library that others can build and relied on asserts executing for your library to be correct, you wrote a bad library.
EDIT: Neither asserts nor these C++26 contract features should be used in a way that requires that they be executed. If you do, you're using them wrong because it is valid for someone to disable them as runtime checks. If the code must run, you should use some other mechanism, I'd recommend an if statement.
Its trivially easy to guarantee that an assert always runs, and its well defined behaviour according to the spec. There's no reason not to if you want to use asserts in a way that guarantees that they always fire, which is a supported use case. Its common practice
There's no equivalent for contracts
You sound as if "my asserts will all always be run via NDEBUG" makes perfect sense and not the exact opposite of what you've expanded it to
> Its common practice
not really, no
post ++11 cpp has been moving away from preprocessor (pedagogically and culturally), so "let's force-undefine NDEBUG" trick isn't at the top of most people's minds
If you want to use asserts, you need to control the definition of NDEBUG. You either do this with your build system (common), or manually (slightly less common). This is literally <assert.h> 101
The preprocessor is widely used for a variety of things when its necessary, including #includes and #defines, because there's literally no other mechanism for this. Its bizarre to say that nobody controls the definition status of NDEBUG because people don't use the preprocessor
There's a whole host of things that libraries need to be extremely conservative about touching. Assert, threads, signals, etc.
To my mind the extent of the contract is that if the user has set NDEBUG then you can assume that assert will be a noop. I don't think you as a library author can make any assumptions about what happens if you set the flag yourself.
There's no difference between the flag being set/unset by your build system, and #define-ing or #undef-ing the symbol in code
that kinda sounds even more insane and cumbersome
And it seems completely sensible that if I'm writing a C++ library that it's header files should include assert.h, and use assert()'s in its inline functions. And you will get no sympathy from me if you break my code by redefining the library behavior of assert().
It's worth noting that the motivation for the above was poorly written libraries that hardcode the use of the builtin assert. So I agree with you completely on that point.
That said I've never been particularly impressed with how assert is defined by the standard and now somehow contracts appear set to be even worse.
It's very bad practice because you have altered the behavior of the standard library.