Validating input

Input validation is a necessary but very tedious task. How many times did you have to write code like the following?

fun setCapacity(cap: Int) { 
    if (cap < 0) { 
        throw IllegalArgumentException() 
    } 
    ... 
}

Instead, you can check arguments with the require() function:

fun setCapacity(cap: Int) { 
    require(cap > 0) 
}

This makes the code a lot more fluent. You can use require() to check for nulls:

fun printNameLength(p: Profile) { 
    require(p.firstName != null) 
}

But there's also requireNotNull() for that:

fun printNameLength(p: Profile) { 
    requireNotNull(p.firstName) 
}

Use check() to validate the state of your object. This is useful when you are providing an object that the user may not have set up correctly:

class HttpClient { 
  ...