[swift-evolution] [Proposal] Add property for negation to Bool

[Erica Sadun]

I'm going to courteously disagree. The not operator belongs on the leading edge and not the trailing edge of the expression:

* One writes ~TruthValue, ¬TruthValue, "not TruthValue", etc. 
* One does not write TruthValue~, TruthValue¬, or "TruthValue not".

Reading code under the current system creates phrases like "if-not expression", naturally conjoining "if not". Under your proposed system, it reads as "if expression not" or "if expression negated truth value". This places a higher cognitive burden on the person reading the code and delays recognition that an expression should be understood in its inverse form. I think it's *more* likely a code reader would miss the intent in scanning than they would miss the leading exclamation point which, although small, is common and often used. As for using a property, such as ".not", ".negativeTruthValue", etc., although it makes the operation bigger and more noticeable, it does so in the wrong place, and inelegantly.

I wouldn't support introducing a `not` keyword as in `if not expression` as this does not feel "Swifty". It is neither concise, or more clear. All in all, this feels like a fix for something that isn't broken, and I cannot see any real world measurable benefit from changing the leading not operator. I believe the impact of the change would be larger than expected and to the detriment of the language.

-- E



> On May 21, 2016, at 8:50 AM, Антон Миронов via swift-evolution <swift-evolution at swift.org> wrote:
> 
> I found negation operator (!) the least detectable among the code. So I’ve decided to add property “not” to BooleanType (Swift 2.2) or Boolean on 3.0 with extension:
> 
> extension BooleanType {
> 	var not: Bool { return !self.boolValue }
> }
> 
> This is code with negation operator:
> 	return !self.lanes[position.y][currentLaneRange].contains(.Gap)
> 
> As I sad before negation operation is hard to spot. Moreover at first it looks like I’m trying to negate self for some reason.
> 
> This is code with “not” property:
> 	return self.lanes[position.y][currentLaneRange].contains(.Gap).not
> 
> Now it is easy to spot the statement I am actually getting negation of.
> On my experience negation operator can occasionally be missed while reading code. This happens less often with “not” property. So I’m proposing to add this property to standard library and prefer it in most cases.
> 
> Thanks,
> Anton Mironov
> 
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