编译时间检查，同时将值传递给 Kotlin Android 中的 function

Question

I am taking a JSON file as input for a class and parsing the values using gson through respective data classes.

I want to call a function that takes a String value as an argument.

The string value allowed is decided from the values parsed from JSON file. Can I somehow check for that string value passed to the function at compile-time & give an error at compile-time?

Or If I can allow only certain values in the argument for the function based on the values from JSON

Detailed Explanation of use case:

I am building a SDK in which a the person using sdk inputs json String. The json is standardised and is parsed in my code.

{
    "name": "Test",
    "objects": [
        {
            "name": "object1",
            "type": "object1"
         }
      ]
}

Here name values and other values may vary based on the input by the developer using it but key remains same. But we need to call a function using the value in objects name parameter.

fun testMethod(objectName:String)

So developer calls the testMethod as testMethod(object1) .

I need to validate object1 parameter based on json but is there any way possible restricting the test method parameter to object1 only & give error at compile time if the developer calls testMethod(obj1)

Right now I parse JSON & have checks inside the testMethod()

Answer 1

Sure it's possible to do, but somehow in different way, that you described. First of all, as you already mentioned this behavior could be done easily. For this purpose we have Objects.requireNotNull() or Guava.Preconditions() . At the same way you can define you checking but this will work on runtime only.

To do in compile time, you need to create Annotation Preprocessor . The same, as did in different libraries, and one of them, could be Lombok , with their NotNull and Nullable . Android annotation just provide mark and bound for IDE warning, but in their case they adding NotNull checking and throw exception for every annotation usage during compile time.

It's not an easy way, but it's what you are looking for.

Answer 2

No, it's impossible check it in compiler time. It's string handling, as numeric calculation.

In my app, I convert string to JSON and JSON to string, passing class descriptor. My aim is record JSON string in a text file to load in SQLite database. This code I've run in my desktop computer not in Android .

data class calcDescr (  
   ...
)
val calc = CalcDescr(...)

 //    toJson:  internal Kotlin data to JSON
val content = Gson().toJson(calc)   

  //==================
  // Testing validity
  // ================

 //    fromJson: JSON to internal Kotlin data. 
 // It needs pass the class descriptor. Uses *Java* token, but it's *Kotlin*
var testModel = Gson().fromJson(content, CalcDescr::class.java) 
 //    toJson:  internal Kotlin data to JSON again
var contentAgain = Gson().toJson(testModel)
//    shoul be equal!
if (content == contentAgain)  println("***ok***")

In my file, I write the variable content in a file