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Struct.put Usage Throws Error

Description

The usage of Struct.put throws a casting error. The following code:

myStruct = { "foo" : "bar" }; result = structReduce( myStruct, function( indexMap, key, value ){ indexMap.put( key, value ); return indexMap; }, {} )


Throws the error:

class java.lang.String cannot be cast to class ortus.boxlang.runtime.scopes.Key

Activity

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Brad WoodFebruary 3, 2025 at 9:45 PM
Edited

I know why this is happening, but don’t have the fix just yet (ran out of time). It’s actually a rather tricky issue in our dynamic interop service where we’re picking the wrong overloaded method. There are actually 3 methods in the byte code called put() for our struct class:

  • put( Key, Object ) - this lives in the struct class

  • put( String, Object ) - this also lives in the struct class, and is what SHOULD have been called

  • put( Object, Object ) - this is a special “bridge” method that the Java compiler inserts just to make our class fully implement the Map interface. All it does is cast the first object to a Key (since that is the generic used) and delegate to our methods)

The core issue is these methods come back from java in random order and we’re just picking the “first one” that matches the arguments. Well, the second two BOTH match the arguments so it’s a toss up which one you get, which explains why the test for this sometimes passes and sometimes fails. And when it finds the 3rd method first is when it fails since that “bridge” method attempts to auto-cast behind the scenes to a Key, thus the error.

This will require a wee bit of refactoring, but once we’re smartly picking the BEST match, not just the FIRST match, then this issue will sort itself.

And for what it’s worth, your code in the ticket is a little presumptive. When calling native java methods on our Struct, the key type is an actual Key instance. Passing a string really shouldn’t expected to work and it’s more of a coincidence that we even have the overloaded version taking a string in this case. Many of the other methods on the struct class only take a proper Key instance. If you pass a Key instance, it will work 100% of the time. This method ambiguity only really exists because we have essentially a

Map<Key,Object>

but you’re passing a java.lang.String as the key which in reality shouldn’t ever happen. The Java bridge method assumes it will always be safe to cast the first arg to a Key, since that’s what’s advertised in the Map generic type.

Jon ClausenJanuary 30, 2025 at 7:06 PM

Actually, You may need to take a look at this. I see there is already a put( String key, Object value ) method in Struct.java so I’m not sure why the interop isn’t using that method.

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Sentry

Created January 30, 2025 at 6:49 PM
Updated February 4, 2025 at 5:30 PM
Resolved February 4, 2025 at 5:30 PM

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