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Comment by jeffbee | Hacker News Reader

In my view this type of system will only be usable by Real Computer Scientists and will completely kill off the workaday hacker. Think of all the people who bitterly complain that a C++ compiler does something unexpected under the banner of UB. That crowd cannot cope with a world in which you have to exactly describe your requirements to an AI. It is also analogous to TDD, so all the TDD haters, which is the overwhelming majority of hackers, are toast.

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I hope you don't mean to imply that TDD haters are not real computer scientists. http://ravimohan.blogspot.com/2007/04/learning-from-sudoku-s...

What’s a workaday hacker and what’s UB?

undefined behavior

UB = undefined behaviour.

You can write code that is valid as in "can be compiled" but outside of C++ standard. It is duty of programmer to not have those, as compiler usually assumes that there's no UB in your code and can do unintuitive things with optimizations.

e.g

  int foo(int8_t x) {
     x += 120
     return x;
  }

  int bar(int8_t y) {
     int z = foo(y);
     if (y > 8) {
         do_important_thing(z);
     }
  }

`do_important_thing` may be optimized out because:

1. signed overflow is a UB. Compiler than assumes that everything passed to foo is less than 8;

2. We pass y to foo => y < 8

3. if branch can then be optimized out

To be pedantic, C has no 8- or 16-bit addition operators, since everything sub-int is scaled up to int to do arithmetic. Therefore, the `x += 120;` line never overflows, since it is actually `x = (int8_t)((int)x + 120);`, and the possible range of `(int)x + 120` is comfortably within the range of expressible ints, while the conversion to int8_t is defined to wrap around when oversized. So there compiler can't optimize out do_important_thing in your example.

This version of the future belongs to the pedants.

Huh, TIL.

I was too lazy to check the exact value of 2^31 and payed for it.

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