[ectoplasm]

If you comment out b, and it segfaults, the segfault is caused by some code in a. Otherwise, the segfault is caused by some code in b. The root cause of the segfault in b may be found in a, but even looking at the stack trace from a debugger will still point you at b. This is nevertheless helpful information.

Further, there's a misunderstanding about the method. You do a binary search on the "percentage" of code viewed as an instruction stream that is allowed to execute, starting from the beginning. I understand that a can have a different length from b. Given more code, you can also search based on timestamps. You never comment out a and allow b to execute without it, this is nonsense. If that's what you thought I meant, I can understand comments about not actually being able to program. I did not explain this clearly, but only because I had forgotten that it was necessary to explain this clearly, because some people actually don't know how to program, even on HN.

[actualprogram]

Let's review the conditions of your example:

  no source,
  no debugger,
  two function calls

And the assertion that // works as a strategy. There's only two things you could possibly comment out, so really the example is not so much "explained poorly" as "conceived poorly". Don't shoot the messenger - it's your example.

As for the further explanation here, allowing a debugger makes the search irrelevant - there's only one piece of information the binary search can tell you: which function causes the segfault, but as you observe, that information's available from the debugger already. And no, it doesn't matter if you reframe things as "a percentage of an instruction stream".

The objection to binary search is not "binary search in the codebase can never tell you anything," it's that it's a method that can't -- not "doesn't" but "can't" -- produce a non-trivial testable hypothesis. Does this mean you can't ever use it? You may have no choice. But it's a terrible place to start, and most of the information it offers is available through other means, often with more precision.