Can we modify += syntax to support modifying neste...

# language-proposals

[jkbbwr]

Can we modify += syntax to support modifying nested immutable containers
e.g.

var a = mapOf(1 to listOf(1, 2, 3), 2 to listOf(4, 5, 6))

I want to propose that a[1] += 4 does the same as a += 1 to a[1]!! + 4