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I'm trying to crate a type-safe groovy-style builder in Kotlin like it's described here. The problem is visibility of lambda receivers in nested lambdas. Here is a simple example.
html {
head(id = "head1")
body() {
head(id = "head2")
}
}
Receiver of the nested lambda is Body that doesn't have the 'head' method. Nevertheless this code compiles and prints into this:
<html>
<head id="head1"></head>
<head id="head2"></head>
<body></body>
</html>
It is expected but is there any way to get compilation error on the inner head?
877
As of Kotlin 1.0 this is not possible. There is an open feature request for this functionality.
167
This is possible since Kotlin 1.1, thanks to the introduction of the @DslMarker annotation.
Here's an example of how it can be used:
@DslMarker
annotation class MyHtmlDsl
@MyHtmlDsl
class HeadBuilder
@MyHtmlDsl
class BodyBuilder
@MyHtmlDsl
class HtmlBuilder {
fun head(setup: HeadBuilder.() -> Unit) {}
fun body(setup: BodyBuilder.() -> Unit) {}
}
fun html(setup: HtmlBuilder.() -> Unit) {}
fun main(args: Array<String>) {
html {
head {}
body {
head { } // fun head(...) can't be called in this context by implicit receiver
}
}
}
See also the documentation at the announcement linked above.
26
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