本文介绍了反射调用函数并使用默认参数的处理方法,对大家解决问题具有一定的参考价值,需要的朋友们下面随着小编来一起学习吧!
问题描述
提供以下功能
fun function(x: Int = 12) {
println("x = $x")
}
如何在不指定x
的情况下使用反射调用它(或者以某种方式使用默认值,不对其进行硬编码)?
How can I using reflection invoke it without specifying x
(or somehow using default value, not hard coding it)?
推荐答案
您可以使用 callBy
,它遵循默认值:
You can use the callBy
, which respects the default values:
::function.callBy(emptyMap()) // is just function()
如果您有许多没有默认值的参数,事情将会变得混乱:
Things will be messy if you have many parameters without default values:
fun foo(a: Int, b: String = "") {}
val ref = ::foo
val params = ref.parameters
ref.callBy(mapOf(params[0] to 1)) // is just foo(1)
如果您的函数是非对象类型的成员函数,或者是扩展函数,或者是作为(其他)非对象类型的成员函数的类型的扩展函数,那将更加无聊.
It will be even more boring if your function is a member function of a non-object type, or it's extension function, or it's an extension function to a type as a member function of a (other) non-object type.
我写了一种减少样板的便捷方法:
I wrote a convenient method to reduce boilerplate:
fun <R> KFunction<R>.callNamed(params: Map<String, Any?>, self: Any? = null, extSelf: Any? = null): R {
val map = params.entries.mapTo(ArrayList()) { entry ->
parameters.find { name == entry.key }!! to entry.value
}
if (self != null) map += instanceParameter!! to self
if (extSelf != null) map += extensionReceiverParameter!! to extSelf
return callBy(map.toMap())
}
用法:
fun String.foo(a: Int, b: String = "") {}
fun foo(a: Int, b: String = "") {}
class Foo {
fun bar(a: Int, b: String = "") {}
fun String.baz(a: Int, b: String = "") {}
}
::foo.callNamed(mapOf("a" to 0))
String::foo.callNamed(mapOf("a" to 0), extSelf = "")
Foo::bar.callNamed(mapOf("a" to 0), Foo())
// function reference don't work on member extension functions
Foo::class.declaredFunctions.find { it.name == "baz" }!!.callNamed(mapOf("a" to 0), Foo(), "")
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