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Other than this particular edge case it's not obvious to me why bitwise operators shouldn't be applicable to boolean values. Aren't they just single-bit vectors

by shawnz 5y ago

Other than this particular edge case it's not obvious to me why bitwise operators shouldn't be applicable to boolean values. Aren't they just single-bit vectors? Of course it makes sense that logical operators wouldn't be applicable to numeric types, but why the reverse?

phkahler 5y ago
>> Other than this particular edge case it's not obvious to me why bitwise operators shouldn't be applicable to boolean values. That is a really good question. At some point they decided that true=1 and false=0 but I'm not sure how deep that goes. In particular what does ! actually do in this context?
- gpderetta 5y ago
  In what context? Unless overloaded ! coerces its operand to bool and returns the negation.
qalmakka 5y ago
If you stop integer values from being implicitly convertible to booleans, you break the language and its compatibility with C. The inverse is debatable, though. I honestly don't see why someone would do bitwise operations on boolean, unless they really wish to die a slow death from thousand cuts. Integer promotion rules make even the simplest operations a wild mess, and there's nothing in the standard that prevents bool from having a sizeof equal to int (thus further complicating everything). It might be sensible for newer language revisions to consider deprecating certain operators from being applied to bool, given that there is a strong change that 99% of the time their use is not on purpose, but I guess it depends on how much disruptive such change would turn out to be.
- shawnz 5y ago
  I don't think the other poster was imagining a language that retained compatibility with C, but rather a new language altogether. Of course it would be impossible to change this aspect of the language if retaining compatibility with C was a requirement. > I honestly don't see why someone would do bitwise operations on boolean For example, you might want the behaviour shown here of not short-circuiting. Or you might want to create a bitwise function that also allows calling on single-bit (i.e. boolean) values.
  - qalmakka 5y ago
    > you might want the behaviour shown here of not short-circuiting. Or you might want to create a bitwise function that also allows calling on single-bit (i.e. boolean) values. In both cases, I think the risk-benefit ratio is way too skewed towards the risk of creating ugly, hard to detect bugs. When I don't want short circuiting from happening, I just assign the RHS of the expression to a variable beforehand; if I want a boolean to become an integer, I make it explicit with a cast. Sometimes, using certain C and C++ debatable features feels like attempting to shave yourself using a dagger. The fact you could do that doesn't mean you should, or even that it is a good idea.
    - gpderetta 5y ago
      You could make the opposite argument that short-circuiting is the surprising behavior [1] and you should make it explicit with an if. [1] and in this very thread many people were actually surprised by it!
      - qalmakka 5y ago
        Short circuiting for logical operators has existed at least since the first C versions in the early '70s. It's maybe not intuitive, it's probably a crummy idea, but that's how basically everything based on C works (including modern languages like Go and Rust), so there's not that much that can be done about that. Also, after seeing how weird JavaScript is in comparison, I have to say that C++ definitely isn't the strangest kid in the block when accounting for weirdness and unintuitive behaviours.

by shawnz 5y ago

phkahler 5y ago

>> Other than this particular edge case it's not obvious to me why bitwise operators shouldn't be applicable to boolean values. That is a really good question. At some point they decided that true=1 and false=0 but I'm not sure how deep that goes. In particular what does ! actually do in this context?

gpderetta 5y ago
In what context? Unless overloaded ! coerces its operand to bool and returns the negation.

qalmakka 5y ago

If you stop integer values from being implicitly convertible to booleans, you break the language and its compatibility with C. The inverse is debatable, though. I honestly don't see why someone would do bitwise operations on boolean, unless they really wish to die a slow death from thousand cuts. Integer promotion rules make even the simplest operations a wild mess, and there's nothing in the standard that prevents bool from having a sizeof equal to int (thus further complicating everything). It might be sensible for newer language revisions to consider deprecating certain operators from being applied to bool, given that there is a strong change that 99% of the time their use is not on purpose, but I guess it depends on how much disruptive such change would turn out to be.

shawnz 5y ago
I don't think the other poster was imagining a language that retained compatibility with C, but rather a new language altogether. Of course it would be impossible to change this aspect of the language if retaining compatibility with C was a requirement. > I honestly don't see why someone would do bitwise operations on boolean For example, you might want the behaviour shown here of not short-circuiting. Or you might want to create a bitwise function that also allows calling on single-bit (i.e. boolean) values.
- qalmakka 5y ago
  > you might want the behaviour shown here of not short-circuiting. Or you might want to create a bitwise function that also allows calling on single-bit (i.e. boolean) values. In both cases, I think the risk-benefit ratio is way too skewed towards the risk of creating ugly, hard to detect bugs. When I don't want short circuiting from happening, I just assign the RHS of the expression to a variable beforehand; if I want a boolean to become an integer, I make it explicit with a cast. Sometimes, using certain C and C++ debatable features feels like attempting to shave yourself using a dagger. The fact you could do that doesn't mean you should, or even that it is a good idea.
  - gpderetta 5y ago
    You could make the opposite argument that short-circuiting is the surprising behavior [1] and you should make it explicit with an if. [1] and in this very thread many people were actually surprised by it!
    - qalmakka 5y ago
      Short circuiting for logical operators has existed at least since the first C versions in the early '70s. It's maybe not intuitive, it's probably a crummy idea, but that's how basically everything based on C works (including modern languages like Go and Rust), so there's not that much that can be done about that. Also, after seeing how weird JavaScript is in comparison, I have to say that C++ definitely isn't the strangest kid in the block when accounting for weirdness and unintuitive behaviours.