Simple and nice way to increment nullable Int in Kotlin

Question

What is the simplest and best readable way to increment nullable Int in Kotlin? Is there any other way than doing this?

var myInt: Int? = 3
myInt = if(myInt!=null) myInt+1 else null

This is quite fine if myInt is simple variable, but it can grow very long when myInt is some longer expression.

crgarridos · Accepted Answer · 2018-10-25T10:15:39.910

21

You can call the operator in its invocable way as:

myInt = myInt?.inc()

Note that the inc() operator does not mutate the value of its receiver but creates a new value. This implies the following statement does not change myInt:

val myInt: Int? = null
myInt?.inc() // myInt still being null

Neither :

val myInt: Int? = 5
myInt?.inc() // myInt still being 5

edited Oct 25 '18 at 10:15

answered Jan 12 '18 at 10:05

crgarridos

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You can also use `myInt?.plus(i)` if you want to increment by an arbitrary amount. – Marv Jan 12 '18 at 10:06
`public val maxFailCount: Integer? = null maxFailCount?.toInt()` Is it ok? – Devendra Singh Oct 25 '18 at 09:47
@DevendraSingh yes, the lines run without error. But try not to use `Integer` class in kotlin. Use `Int` instead. IntelliJ also warns you about this. – Sourav Kannantha B Dec 12 '20 at 07:41

score 3 · Answer 2 · answered Jan 12 '18 at 10:17

3

The other answers present shorter alternatives, I'll present how to properly use the basic if-construct:

var myInt: Int? = 3
if (myInt != null) myInt++

It's much like in Java, you don't have to add any new layer of complication.

answered Jan 12 '18 at 10:17

Marko Topolnik

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score 0 · Answer 3 · answered Jan 12 '18 at 10:06

0

Use inc. In Kotlin, all the operators are converted into method call. See here for more details.

var myInt: Int? = 3
myInt = myInt?.inc()

answered Jan 12 '18 at 10:06

Joshua

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score 0 · Answer 4 · answered Jan 12 '18 at 10:07

var myInt: Int? = 3
myInt = myInt?.inc()

Note that I've assigned the value returned by inc() to myInt, as documentation states the following:

The inc() and dec() functions must return a value, which will be assigned to the variable on which the ++ or -- operation was used. They shouldn't mutate the object on which the inc or dec was invoked.

score 0 · Answer 5 · answered Jan 12 '18 at 10:10

0

The best solution is crgarridos' one.

Here is an alternative in case you want to increment by other values:

var myInt: Int? = 1
val n = myInt?.plus(1)
println(n)

This prints:

answered Jan 12 '18 at 10:10

gil.fernandes

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Simple and nice way to increment nullable Int in Kotlin

5 Answers5