kotlin 为什么构造函数的参数可以加上var val修饰，而普通函数就不行呢？

Question

kotlin 为什么构造函数的参数可以加上var val修饰，而普通函数就不行呢？

Answer 1

早期的 Kotlin 版本函数参数是可以定义成 var 的，不过后来官方明确了「函数参数都是不可变」这一点。在这篇更新日志里可以找到说明：

The main reason is that this was confusing: people tend to think that
this means passing a parameter by reference, which we do not support
(it is costly at runtime). Another source of confusion is primary
constructors: “val” or “var” in a constructor declaration means
something different from the same thing if a function declarations
(namely, it creates a property). Also, we all know that mutating
parameters is no good style, so writing “val” or “var” in front of a
parameter in a function, catch block of for-loop is no longer allowed.