I have a function with lambda parameter:
private fun MyFun(
progress: () -> Float,
) {
// ...
}
I want to annotate return value of progress lambda with @FloatRange(from = 0.0, to = 1.0), but can't figure out how to do this. All my attempts to solve this causes syntax errors. Where am I wrong?
You can define a functional interface to describe your type, and annotate it there:
fun interface ProgressCallback {
@FloatRange(from = 0.0, to = 1.0) fun progress(): Float
}
private fun myFun(progress: ProgressCallback) {
// ...
}
fun foo() {
myFun { 5.0f } // error, doesn't conform to FloatRange
}
FYI, lint is not sophisticated enough to detect a failure to meet the requirement if you pass a function reference instead of a lambda, or if you indirectly call a function that returns a Float:
fun bar() = 5.0f
fun foo() {
myFun(::bar) // no error
myFun { bar() } // no error
}
Or if you return anything besides a single literal value:
fun foo() {
myFun { 1.0f * 2.0f } // no error
}
In kotlin language, lambda to perform a task, not to annotate. You can comment code likes this // FloatRange(from = 0.0, to = 1.0)
example :
// FloatRange(from = 0.0, to = 1.0)
private fun MyFun(
progress: () -> Float,
) {
}
you can read here to better understand lambda in kotlin language