Boolean extension function

Question

When I try to create Extension Function to set Boolean true or false like the below.

Boolean.setTrue(){
 this = true
}

Boolean.setFalse(){
 this = false
}

It says variable expected. How to achieve this.

Generally you would be making the code less readable by not following the usual conventions. Either way it doesn't matter since you can't ever change the value of `this`, extension function or not. — Pixel Elephant, Aug 29 '17 at 19:12
compare to `!someBoolean`, `someBoolean.not()` looks readable right. That the way I tried this. But now I underStood the concept. — Bhuvanesh BS, Aug 29 '17 at 19:17
To add, if you could redefine this you could use that to make a constructor possibly return not an instance of the class it is the constructor for, which would really confuse code (in plain Java if you could do that you could even make a constructor which returns null, which would really break a lot of normally safe assumptions) — jrtapsell, Aug 29 '17 at 19:17
Related: https://stackoverflow.com/questions/7979623/why-is-assignment-to-this-not-allowed-in-java — BakaWaii, Aug 30 '17 at 03:22
Hey guys, Bhuvanesh asked something that is totally feasible in C#, Swift... — Luc-Olivier, Jul 20 '19 at 16:25

score 6 · Accepted Answer · answered Aug 29 '17 at 19:23

You cannot change the value of this, this would break a lot of assumptions, even if you could you would not be able to change the value, as Booleans are immutable.

More generally, there is a fine line between simplifying code, and making it more complex, and in this case that would complicate it. I would agree that adding String.splitByDot() may make sense, but replacing idiomatic code tends to just make the code more complex, as you start to wonder why the code had to be replaced.

s1m0nw1 · Answer 2 · 2017-08-30T06:10:40.730

Sorry but this does not make sense. Just use myBool=false, it's what anyone understands and cannot get any more readable. Also Boolean is immutable and what you're trying isn't possible anyways.

We have to be careful not to overuse extensions. It's one of the greatest features Kotlin (and others) offers, but in certain examples, e.g. trying to change the way a dead simple Boolean is being assigned, it's getting dangerous IMHO (luckily it's not possible).

score 3 · Answer 3 · answered Jun 25 '18 at 23:23

Here is an extension method that works in C# 7.2 or later:

public static class Extensions
{
    public static bool Toggle(ref this bool b) => b = !b;
}

Then elsewhere, something like this will work:

bool     b1 = true; // Works for primitive bool type.
Boolean  b2 = true; // Works for Boolean object, too.
b1.Toggle(); 
b2.Toggle();

The only benefit I see to using an extension method is to shorten lines with long bool expressions, such as replacing:

this.SomeObjectWithALongName.SomeVerboselyNamedProperty
   = !this.SomeObjectWithALongName.SomeVerboselyNamedProperty

with

this.SomeObjectWithALongName.SomeVerboselyNamedProperty.Toggle();

I don't know what drawbacks this extension method may have.

score 2 · Answer 4 · answered Aug 29 '17 at 19:14

2

The reason you can't do this is that you cannot reassign the receiver in an extension function.

It's not possible to change the value of the Boolean because it is immutable.

answered Aug 29 '17 at 19:14

JK Ly

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score 0 · Answer 5 · answered Jul 20 '19 at 16:41

0

The reason you can do this comes to a lack of implementation of Kotlin extension probably due to the fact Extension in Kotlin are resolved Statically (even probably really static). So 'this' in a static context doesn't make sense.

answered Jul 20 '19 at 16:41

Luc-Olivier

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Boolean extension function

5 Answers5