Converting a generic function to Kotlin fails

Question

I'd like to rewrite some of my code to Kotlin. I pasted the working code first to show the origin.
I tried

The following is a working excerpt written in Java:

Function1.class (part of a framework):

public interface Function1<T1, R> {
    R call(T1 var1);
}

Authmanager.class:

public boolean isAuthed() {
    Boolean isAuthed = getWithAuthPolicyManager(
            authPolicyManager -> authPolicyManager.getBoolean(IS_AUTHED)
    );

    if (isAuthed != null) {
        return isAuthed;
    } else {
        return false;
    }
}

public <T> T getWithAuthPolicyManager(@NonNull Function1<AuthManager, T> function) {
    Objects.requireNonNull(function);
    synchronized (AUTH_POLICY_LOCK) {
        try {
            openAuthPolicyManager();
            return function.call(authPolicyManager);
        } catch (OpenFailureException | EncryptionError e) {
            LOGGER.error("Error:", e);
            return null;
        } finally {
            authPolicyManager.close();
        }
    }
}

I would like to rewrite it to Kotlin but I cannot:
Authmanager.kt

fun isAuthed(): Boolean {
    val isAuthed =
        getWithAuthPolicyManager<Boolean>({
            authPolicyManager -> authPolicyManager.getBoolean(IS_AUTHED) 
        })
    return isAuthed ?: false
}

fun <T> getWithAuthPolicyManager(function: Function1<AuthManager, T>) : T? {
    synchronized (AUTH_POLICY_LOCK) {
        return try {
            openAuthPolicyManager();
            return function.call(authPolicyManager);
        } catch (OpenFailureException | EncryptionError e) {
            LOGGER.error("Error", e);
            null;
        } finally {
            authPolicyManager.close();
            null
        }
    }
}

Actually, I just copy-pasted the Java code to the Kotlin class to automatically convert to Kotlin. However, the linter says:

Type mismatch.  
Required: Function1<AuthManager, Boolean>  
Found:    (AuthManager) -> Boolean!

to this line getWithAuthPolicyManager<Boolean>({authPolicyManager -> authPolicyManager.getBoolean(IS_AUTHED)}) in fun isAuthed().

Do you have any idea how this could be fixed?

Pawel · Accepted Answer · 2018-10-14 13:25:09Z

1

Your second function is not converted at all, it still Java code. I used converter from try.kotlinlang.org and got the following code:

fun <T> getWithAuthPolicyManager(function : Function1<AuthManager, T>) : T? {
  synchronized (AUTH_POLICY_LOCK) {
    try
    {
      openAuthPolicyManager()
      return function.call(authPolicyManager)
    }
    catch (e : OpenFailureException) {
      LOGGER.error("Error", e)
      return null
    }
    catch (e : EncryptionError) {
      LOGGER.error("Error", e)
      return null
    }
    finally
    {
      authPolicyManager.close()
    }
  }
}

After light cleanup it should look like this:

inline fun <T> getWithAuthPolicyManager(function : (AuthManager) -> T?) : T? {
  synchronized (AUTH_POLICY_LOCK) {
    return try
    {
      openAuthPolicyManager()
      function(authPolicyManager)
    }
    catch (e : OpenFailureException) {
      LOGGER.error("Error", e)
      null
    }
    catch (e : EncryptionError) {
      LOGGER.error("Error", e)
      null
    }
    finally
    {
      authPolicyManager.close()
    }
  }
}

Please look into doing Kotlin tutorial if you can't tell Kotlin and Java function declarations apart.

edited Oct 14, 2018 at 13:25

answered Oct 14, 2018 at 13:18

Pawel

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2 Comments

roncsak Over a year ago

Mea culpa, I copy-pasted the second Kotlin function wrongly to here. Thanks for spending your time on it, anyway! However, the problem still stands. Do you have any idea ? (function calls in getWithAuthPolicyManager() contains non-public-API calls, so I cannot make it an inline function)

roncsak Over a year ago

Also changing function : Function1<AuthManager, T> to function : (AuthManager) -> T? solved the problem! Thanks!

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