properties - Kotlin extension function on mutable property -

i'm trying set extension function on mutable property can reassign property in extension function. wanted know if possible.

my goals make date extensions easy access. example:

fun date.adddays(nrofdays: int): date {     val cal = calendar.getinstance()     cal.time =     cal.add(calendar.day_of_year, nrofdays)     return cal.time } 

this function adds number of days date using calendar object. problem each time have return new date can confusing reassign each time use function.

what i've tried:

fun kmutableproperty0<date>.adddays(nrofdays: int) {     val cal = calendar.getinstance()     cal.time = this.get()     cal.add(calendar.day_of_year, nrofdays)     this.set(cal.time) } 

unfortunately can't used on date object.

is possible this?

unfortunately, cannot define extension on member property , call fluently in kotlin 1.0.3.

your extension can rewritten work this:

fun <t> kmutableproperty1<t, date>.adddays(receiver: t, nrofdays: int) {     val cal = calendar.getinstance()     cal.time = this.get(receiver)     cal.add(calendar.day_of_year, nrofdays)     this.set(receiver, cal.time) } 

with following usage:

class c(var date: date) { ... } val c = c(somedate())  c::date.adddays(c, 123) 

with bound callable references (likely supported in kotlin 1.1) possible following syntax:

c::date.adddays(123) 

---

as @marcinkoziński suggests, can mutate date objects without reassigning property:

fun date.adddays(nrofdays: int) {     val cal = calendar.getinstance()     cal.time =     cal.add(calendar.day_of_year, nrofdays)     this.time = cal.timeinmillis } 

with usage:

class c(var date: date) val c = c(somedate())  c.date.adddays(123) 

with solution, have control references date object mutated. solution works mutable objects, though not suitable property storing immutable ones.