Treating Non-Boolean Types as Logic Values

Date: 26-Oct-2009/22:29


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Historically, I have always disliked the idea of using boolean test operations on types that can take a number of values. This deep-seated aesthetic grudge comes from cases like this:
int x = 0;
if (not x)
   cout << "X is zero" << endl;
I'm simply bothered by this. Perhaps it's a cognitive thing where I just don't feel there's any "truth" to the idea that every non-zero integer is somehow "true" but zero is somehow "false". It could just as easily be that negative numbers are false and non-negative numbers are true. Or if you ask a mathematical purist, they might suggest that at a more foundational level it is primes that are true and non-primes are false!
My comfort zone is when I'm only testing for "truth" and "falsehood" those things that can only have the values true and false. If I could, I would enforce this. So in the example above I would always write something more like:
int x = 0;
if (x == 0)
   cout << "X is zero" << endl;
That particular example is not very controversial, and I think most programmers would agree with me that's a better way to test against a literal zero. It's just better code for capturing the intention.
Yet I have historically considered that a logical extension of "zero is not false" is the premise that "null pointers are not false". And that belief is contrary to practice:
shared_ptr< foo > fooPointer;
if (not fooPointer)
   cout << "fooPointer is null" << endl;
In fact, look what a mouthful you get if you insist on comparing against null literally:
shared_ptr< foo > fooPointer;
if (fooPointer.get() == nullptr)
   cout << "fooPointer is null" << endl;
In the past I have tried to work around this by creating inline template wrappers like "isNull()" so that I could stick to my guns and avoid flattening pointers into booleans. It doesn't cost any more in the runtime, so I figured what's the harm?
template< class T > inline bool isNull(shared_ptr< T > ptr) {
  return !ptr;
Yet I've decided this is a lost cause and too much of a speed bump in sharing my code with other C++ programmers. They've accepted the notion that null pointers are false and non-null pointers are true, and you use boolean logic to test this—not some other operator. It's not worth it to pick this particular fight.
I'm not happy about it. But I now accept this for pointers only. And I'm going to use "not" instead of "!"... it's part of the language and a lot more readable.

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