nullable - Make Kotlin warn on assignment of flexible/platform type to non-null type? -


when calling non-nullability-annotated java function kotlin, flexible-typed return values, denoted exclamation marks, e.g. string!.

kotlin silently allows assigning these flexible values normal non-null type, e.g. string, can cause nullpointerexceptions @ runtime.

i prefer compiler warnings or errors such assignments. alternatively, treat platform types equivalent nullable types (e.g. string?).

as example, java code:

import android.os.systemclock; import android.support.annotation.nonnull; import android.support.annotation.nullable;  public class nulltest {      private string maybe() {         if (systemclock.elapsedrealtimenanos() % 2 == 0) {             return null;         }         return "ok";     }      public string annotatednothing()            { return maybe(); }     @nullable public string annotatednullable() { return maybe(); }     @nonnull  public string annotatednonnull()  { return "ok"; }  }

...and following kotlin code, i'd errors on 2 new lines (see comments):

fun testnulls() {     val obj = nulltest()      val nullexact: string  = obj.annotatednullable() // gives error     val nullmaybe: string? = obj.annotatednullable()     val nullinfer          = obj.annotatednullable()      val okayexact: string  = obj.annotatednonnull()     val okaymaybe: string? = obj.annotatednonnull()     val okayinfer          = obj.annotatednonnull()      val bareexact: string  = obj.annotatednothing() // want compiler error here     val baremaybe: string? = obj.annotatednothing()     val bareinfer          = obj.annotatednothing()      print("length " + nullexact.length)     print("length " + nullmaybe.length) // gives error     print("length " + nullinfer.length) // gives error      print("length " + okayexact.length)     print("length " + okaymaybe.length) // gives error     print("length " + okayinfer.length)      print("length " + bareexact.length)     print("length " + baremaybe.length) // gives error     print("length " + bareinfer.length) // want compiler error here }

the point force me add null checks or !!, making sure @ least have explicit it.

is possible?

in comments of 2014 jetbrains blog post, when introduced platform/flexible types, sounds planning add option warn these situations, haven't been able find further information on that.

the kotlin documentation describes exact case:

any reference in java may null, makes kotlin's requirements of strict null-safety impractical objects coming java. types of java declarations treated specially in kotlin , called platform types. null-checks relaxed such types, safety guarantees them same in java

unfortunately, means there no way issue warning during compilation time. silver lining kotlin @ least prevent null propagation in runtime.

when call methods on variables of platform types, kotlin not issue nullability errors @ compile time, call may fail @ runtime, because of null-pointer exception or assertion kotlin generates prevent nulls propagating

if don't control source code of java library use, treat of results potentially nullable, unless evident not.


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