Proposal: is not syntactic sugar

[TheUnlocked]

I get that this is somewhat frivolous, but I think that

if (foo is not Bar){
     // Do something
}

is cleaner than

if (!(foo is Bar)){
     // Do something
}

I can't really think of any downsides to doing this, other than that it would take any amount development time for a relatively inconsequential syntax change. There are upsides however:

1. It's more English-like.
2. It doesn't require surrounding anything in parentheses, slightly reducing the amount of time you need to put into negating an is expression.
3. In larger boolean expressions, it may decrease parenthesis clutter.

An alternative to is not could be is! or !is, though those could be somewhat confusing.

[HaloFour]

Related to #882 and #568. This particular syntax has been suggested in some comments. However, I think that it would have to somehow work alongside pattern matching in order to fit with the is operator.

[MkazemAkhgary]

public class not {}

if(obj is not not)

I can't really think of any downsides to doing this

1- obj is not of type not

2- obj is of type not and variable not is declared with pattern matching

[Unknown6656]

@MkazemAkhgary : In this case one would have to provide either an alias or the parent namespace name, e.g.:

namespace kek
{
    public class not {}
    

    public static class Program
    {
        public static int main(string[] argv)
        {
            ...
            if(obj is not kek.not)
            ...
        }
    }
}

---

I do not think that that would be a bad solution, as one does rarely name a class not:
It is against the standard C# naming convention and it is pretty non-descriptive (except e.g. when it represents a not-opcode in a compiler or something like that).

[lachbaer]

This came up already so often, but somehow I got the feeling that it is the word not that hinders the construct to make progress in its career 😉 . I'll throw in leaving the C-ish ! char for the meaning of not:

if (foo is ! Bar) { ... }

(this acutally looks a bit spanish ¡s! 😁 )

[Neme12]

I'd be for this if not is actually a recursive pattern (as opposed to an extension of is), so it would be possible to use case not Bar b for example.

[MkazemAkhgary]

I don't think not is really helping here. it just gives vague meaning. case not is definitely vague, if there are 2 case not then which one should be chosen if given argument is neither of two cases?

you cant have more than one case not and there is already default case for this purpose.

english language is not a programming language.

[gafter]

Order is significant in a switch statement. The first matching case is taken. If none match then a default label, if present, is taken.

[Richiban]

Having not as a way of inverting a pattern could prove to be incredibly useful, especially in recursive situations. E.g.

switch(point)
{
    case Point2D(not 0, not 0): ...
    case not Point3D(_, _, _): ...
    default: ...
}

[Neme12]

@Richiban yes it would be useful especially in recursive patterns... but this of course begs the question: what if you want to match if the value is > 0? or any other comparison? would this feature be a dead end?

[Neme12]

but of course inverting a pattern is a much more general concept than inequality...

i'm just a little worried that in this particular case (of Point(not 0, not 0) it might not be so much useful after all/ it would have a very narrow use case because:
a) it would only work if you want inequality
b) you can't extract the value this way

that said, i would still prefer this as a general pattern rather than some syntactic sugar around is (in fact i don't think i want such a feature at all, this doesn't feel right to me to make another version of is just to have a nice word in there and make it read well in 1 very specific case, and a make new contextual keyword for that)

[deniszykov]

There is syntax for this:

if (foo is Bar == false) {
     // Do something
}

[Neme12]

how about foo is Bar is false 😄 (also existing syntax)

[MkazemAkhgary]

how about

dear computer, see if foo is bar, then do this.

yes, a little exaggeration, just to show you my feelings about 1-It's more English-like.

[yaakov-h]

This is csharplang, not applescriptlang 😄

[TruePluto]

@MkazemAkhgary How about using "isnot" instead of "is not"

public class not {}

if(obj isnot not)

[jnm2]

I like is not, not as much isnot, and I still like the informality of isnt. The potential standalone not pattern seems the most interesting though.

[gafter]

Added #1350 to champion this idea as a pattern form, along with some previous suggestions from @alrz.

[CyrusNajmabadi]

If it starts with i, it's an interface, and thus should be written ISnot. I.e. the set of functionality in things that are snot-like.

[gafter]

@CyrusNajmabadi Since @jnm2 likes informality, I think we should go with aint.

[jnm2]

@CyrusNajmabadi If my nose was running money...

[sharwell]

Duplicate of #27

[gafter]

Already championed as part of #1350

[AustinBryan]

Personally, I think this is much cleaner:

if (foo aint bar)
{

}

😜

[TheUnlocked]

Closing because this was championed a while ago.