[robotresearcher]

That’s what the ‘is’ is for. If you have a ‘?’ character, you don’t need it. But tastes vary. I don’t even like the ‘is’.

1. if isValid() 2. if valid?() 3. if isValid?() 4. if valid()

Number 4 is nicest to my eyes. But I guess if the ‘?’ or ‘is’ (or both) is a promise to the user that the function is a true predicate, then I can see its utility.

[TeMPOraL]

'?' / 'is' get more useful with more complex predicate names than just 'valid', and they also help with certain corner cases in English. For example, what does the following code do:

  if(widget.free()) { ... }

Does it 1) check if the widget is "free" (whatever that means in the widget domain), or 2) frees the widget and checks the outcome of that operation?

If I saw something like this while reading code, I'd pause and carefully check what exactly is going on here.

In fact, I was going to write "Option 2) resembles resource management patterns, for example memory management in C", but then I checked and noticed that free() in C does not return a value, so this pattern would not exist with malloc()/free() - in other words, despite doing a bit of C and a lot of C++ in the past two decades, I still tripped over this.

Now compare with:

  if(widget.isFree()) { ... }
  if(widget.free?()) { ... }

Both resolve this ambiguity.

On that note, I'd love some kind of sigil for "asserting" functions - which are similar to checks, but instead of returning true/false, they ensure the argument is in the state described by the function name, or else they throw an exception. It's a pattern I've been using in exception-ful code to cut down on noise. For example:

  // Check if connected; if not, maybe run reconnection
  // logic or attempt some other form of recovery.
  // The only way control proceeds past this line is if
  // the session is connected; if it isn't and can't be,
  // exception is thrown.
  EnsureConnected(session);
   
  if(IsSomething(session, arg1)) {
    // ... some code requiring connected session
  }
  // ... more code requiring connected session

It's not a big deal, but in some cases, that "Ensure" or "Assert" look weird, and I don't like inventing more synonyms for the same pattern.

[Joker_vD]

> Does it 1) check if the widget is "free" (whatever that means in the widget domain), or 2) frees the widget and checks the outcome of that operation?

Just program in Esperanto! So 1) would be "umo.libera()" and 2) be "umo.liberigu()".

I can't believe I still remember the grammar after what, 10 years of complete disuse?

[robotresearcher]

Good points.

I’d avoid overloading a standard library function name like free().

Your request for syntax for assertions reminds me of the ‘guard’ keyword in Swift, which is good for making sure of preconditions.