Let‘s see following code:
println(colors.reduce { acc, curr -> "$acc, $curr" }) // red, blue, green, black val myMap = mapOf(1 to "one", 2 to "two", 3 to "three") myMap.filter {(k, v) -> v.startsWith("t")}.forEach {(k,v) -> println("$k $v")}
Why in "reduce" we don‘t need to add ()
but in "filter" example we need?
Answer is in "reduce" it is a function take two params, which doesn‘t require ()
in "filter" it means destructing, in fact, you can write:
myMap.filter { item -> item.value.startsWith("t")}.forEach {item -> println("${item.key} ${item.value}")}
[Kotlin] When to add () and when not to
原文：https://www.cnblogs.com/Answer1215/p/13879118.html