Hello Can someone tell me why can t I do this

Question

Miguel · Answer

Since I am defined a generic return type shouldn t I be allowed to return anything

Shawn · Answer

No that s not how generics are used

Shawn · Answer

If you want to return anything your return signature would be `List lt Any gt `

Shawn · Answer

a generic constraint allows you to return the type specified by the enclosing class or at the call site

Miguel · Answer

But I what if I want to allow things like `val x Date = lol 13 02 2018 Date class java ` thinking face

Shawn · Answer

That doesn t contradict what I ve said If `lol ` returns a different type based on the class you pass to it you can still use generics

Shawn · Answer

for a `fun lt T gt lol T` you d get a `Date` out of it by calling like this `lol lt Date gt `

Shawn · Answer

if you need the `Class lt T gt ` from it use `reified`

Shawn · Answer

``` inline fun lt reified T gt lol ```

Miguel · Answer

I already searched that option but I call some private methods on that function so I can t use it

Shawn · Answer

Well you could potentially delegate out to another public method that isn t `inline` but the better question at this point really is what are you trying to do

Miguel · Answer

What I want to achieve is this I want to build a collection of objects by parsing a string representation of them that has a fixed length In this case I want to be able to parse ` 2 2 ` gt Int and ` 27 03 2017 28 03 2017 ` gt LocalDate Ideally I would want a function `fun lt T gt fromString elementsString String classValue Class lt T gt List lt T gt ` that receives the string representation and returns the list of elements which can be a list of 2 Ints or a list of 2 LocalDates

Miguel · Answer

That sort of explains the image I sent you I have another 2 functions that return a nullable type indicating if they could parse 2 ints or 2 dates respectively So in my head I m imagining the `fromString` function to call the parseInt function and returning that and only calling the parseDate if the other one was not well succeeded

Miguel · Answer

sorry if it wasn t very clear at first what I was trying to achieve

Shawn · Answer

how do you plan on calling this function If you know what the types are beforehand why not just overload the function have one that accepts two dates strings and one that accepts two ints

Miguel · Answer

Ideally I would plan on calling like `val x List lt Int gt fromString 2 2 Int class java `

Miguel · Answer

Well I do the know the types beforehand but that would originate repeated code for every type I would want to implement There is a core logic that I kind of want to maintain in `fromString` and I would like to delegate the responsibility of parsing to the wanted type to some other function

Shawn · Answer

hm I don t think there s a great way to do it without an unchecked cast at some point unfortunately

Shawn · Answer

something kinda like this <http kotlinlang org docs reference inline functions html reified type parameters>

Miguel · Answer

Oh I see Thank you very much Shawn Merry christmas if you celebrate it

Shawn · Answer

No problem Merry Christmas to you too

Pavlo Liapota · Answer

< Miguel> I agree with < Shawn> that if you know the type then it is better to have separate function for each type supported by you But all common logic during parsing you can have in one generic function so no code duplication See example here

Miguel · Answer

Thanks < Pavlo Liapota>