[Question] Using `Dict` as a function return type with string values.
hulto opened this issue · comments
This is dumb question but I'm having a hard time using the Dict or SmallMap<Value, Value> types as a return type for rust functions. Specifically when trying to return a Value holding a string.
- I see in this issue the suggestion to use the evaluator heap. Is it recommended to pass a reference to the eval heap in each functions and perform allocations there?
- Is there a better way in general to return a Map / dictionary from a starlark function?
Here's a test function i'm trying to add to the starlark library given a string, it should return a list of dictionary objects using Value<String> as the keys and values.
I'm able to use the frozen string value, and int but having issues with non-constant strings.
Thank you
You allocate a value in temporary heap, and then try to destroy in while returning a value owned by that heap. This is incorrect because memory would be freed when function returns.
If you need to return a heap allocated value, create a heap outside and pass a heap reference to the function.
Is there a better way in general to return a Map / dictionary from a starlark function?
Are you talking about native functions, generated with #[starlark_module]? It is not clear from your example.
Thanks for the quick reply!
Are you talking about native functions, generated with #[starlark_module]? It is not clear from your example.
Yes sorry i am working on a function generated with #[starlark_module]
If you need to return a heap allocated value, create a heap outside and pass a heap reference to the function.
Makes sense. I tried to define a heap outside the function and pass a reference in. I ran into issues with what context the heap needs to live in.
Here's my first attempt seems like I need to have the heap defined outside this function. Makes sense.
After that I tried moving it outside to a higher context.
I experimented with some different closures but had a number of issues.
My understanding is that the #[starlark_module] macro is doing some rearranging and the defined functions are essentially anonymous and unable to inherit the context.
I looked at maybe passing the GlobalsBuilder heap in but I see that's a frozen heap.
How should I be passing the heap reference? Should I be using lifetimes to explicitly manage tmp_heap?
Updated function code to use heap reference.
How should I be passing the heap reference?
If this is a function inside #[starlark_module], like test_func_starlark in your example above, you just add &'v Heap parameter, and that's it.
Here is an example in repo test:
That is incredibly cool. Thank you 🙂
The correct code looks like this if anyone else reads this.
