In Kotlin, a receiver is the value on which an extension function or receiver lambda operates. The receiver type names the type being extended; the receiver object is the instance supplied at the call site. section 3.3 section 13.2.1
An extension function receiver
fun String.lastChar(): Char = get(length - 1) println("Kotlin".lastChar()) // n String is the receiver type, and "Kotlin" is the receiver object. Inside lastChar, the receiver is available as this, although Kotlin normally lets you omit it. The function can use public members of String but cannot access private or protected members. section 3.3
Receiver syntax also supports configurable blocks:
- A receiver lambda changes (StringBuilder) -> Unit into StringBuilder.() -> Unit. The supplied StringBuilder becomes the lambda's implicit this. section 13.2.1
- Inside a receiver lambda, members can be called directly: append("World!") is shorthand for this.append("World!"). section 13.2.1
- From Java, an extension function appears as a static method whose first argument is the receiver object, such as StringUtilKt.lastChar("Java"). section 3.3.2
package strings fun String.lastChar(): Char = this.get(this.length - 1)
Inspect the compact declaration showing the receiver type before the extension function name and receiver members used in the body. section 3.3
