TL;DR: Zig injects checks and aborts the program at runtime unless you specify that you wish to ignore the problem. This can be done explicitly within the code or by compiling under a build mode that ignores checks (unless specified manually).
Programs compiled as Debug and ReleaseSafe will terminate at runtime if UB is triggered. Compiling for ReleaseSmall and ReleaseFast will cause traditional C-style UB. If you care about your program doing what it's supposed to do, you use ReleaseSafe. Doing Release[Fast|Small] will do something similar to -O3 in other languages, which will often change behaviour.
Note, however, that you can compile your code under "just allow UB and see what happens" mode but still benefit from checked UB by setting @setRuntimeSafety(true); this will introduce the assertions despite the unsafe build modes you may specify.
It's like introducing a C++ compiler flag* telling the compiler "ignore exceptions and just continue". You know you're in for a bad time the moment you specify it, but it makes your program blazingly fast because it greatly reduces the amount of code to generate/checks to execute.
The main advantage of checked UB is that well-tested code can make use of the unchecked nature of these features for speed without having length check code blocks that need to be wrapped in debug #ifdefs or similar. Assuming you don't run test builds with checks enabled (and why wouldn't you) you'd catch these problems in your build pipeline.
This is different from the normal way of working with C and friends, where UB remains in debug/-O1 builds but just acts a little differently. Some compilers will insert breakpoints, others will ignore the problem like in release mode, nobody knows what will happen and your compiler can't detect this problem for you.
* note that -fno-exceptions exists, but that aborts the program rather than let it continue.
TL;DR: Zig injects checks and aborts the program at runtime unless you specify that you wish to ignore the problem. This can be done explicitly within the code or by compiling under a build mode that ignores checks (unless specified manually).
Programs compiled as Debug and ReleaseSafe will terminate at runtime if UB is triggered. Compiling for ReleaseSmall and ReleaseFast will cause traditional C-style UB. If you care about your program doing what it's supposed to do, you use ReleaseSafe. Doing Release[Fast|Small] will do something similar to -O3 in other languages, which will often change behaviour.
Note, however, that you can compile your code under "just allow UB and see what happens" mode but still benefit from checked UB by setting @setRuntimeSafety(true); this will introduce the assertions despite the unsafe build modes you may specify.
It's like introducing a C++ compiler flag* telling the compiler "ignore exceptions and just continue". You know you're in for a bad time the moment you specify it, but it makes your program blazingly fast because it greatly reduces the amount of code to generate/checks to execute.
The main advantage of checked UB is that well-tested code can make use of the unchecked nature of these features for speed without having length check code blocks that need to be wrapped in debug #ifdefs or similar. Assuming you don't run test builds with checks enabled (and why wouldn't you) you'd catch these problems in your build pipeline.
This is different from the normal way of working with C and friends, where UB remains in debug/-O1 builds but just acts a little differently. Some compilers will insert breakpoints, others will ignore the problem like in release mode, nobody knows what will happen and your compiler can't detect this problem for you.
* note that -fno-exceptions exists, but that aborts the program rather than let it continue.