[cpp-ue4] Fix generated code not compiling when using unique array items

[roseatromero]

Currently if the "uniqueItems": true, is present in the schema for array items, the generated code does not compile due to lack of support for TSet container

0>GenericApiOperations.cpp(151): Error C2672 : 'CollectionToUrlString_multi': no matching overloaded function found
0>Helpers.h(203): Reference  : could be 'FString ::CollectionToUrlString_multi(const TArray<T,FDefaultAllocator> &,const TCHAR *)'
0>GenericApiOperations.cpp(151): Reference  : 'FString ::CollectionToUrlString_multi(const TArray<T,FDefaultAllocator> &,const TCHAR *)': could not deduce template argument for 'const TArray<T,FDefaultAllocator> &' from 'const TSet<FString,DefaultKeyFuncs<InElementType,false>,FDefaultSetAllocator>'
0>        with
0>        [
0>            InElementType=FString
0>        ]

This PR adds a template that correctly combines the URL parameters for associative container TSet and fixes the compilation issue.

Testing:

Based on the following schema:

"schema": {
    "pattern": "^[^/\\\\]*$",
    "uniqueItems": true,
    "type": "array",
    "items": {
      "type": "string"
    }
  }

I verified in the debugger that the URL parameters were added

[roseatromero]

Tagging @Kahncode for visibility

[Kahncode]

Hello @roseatromero thanks for the change.

I feel like this is perhaps a more ambitious direction than I would have taken. Perhaps less correct, but I would have handled "set" as TArray. But I don't understand where the set comes from here, your schema has clearly an Array, so why does it translate to TSet?

Anyway the change I would suggest is in the file CppUE4ClientCodegen.java to change
typeMapping.put("set", "TSet");
to
typeMapping.put("set", "TArray");
as TArray can contain a set of elements after all.

[roseatromero]

Hello @roseatromero thanks for the change.

I feel like this is perhaps a more ambitious direction than I would have taken. Perhaps less correct, but I would have handled "set" as TArray. But I don't understand where the set comes from here, your schema has clearly an Array, so why does it translate to TSet?

Anyway the change I would suggest is in the file CppUE4ClientCodegen.java to change typeMapping.put("set", "TSet"); to typeMapping.put("set", "TArray"); as TArray can contain a set of elements after all.

TSet is an associative rather than a sequence container, that guarantees the items stored inside are unique - hence why it's correctly generated to use it when uniqueItems is set to true. With TArray there could be duplicates in the generated URL params, which is not what the API is expecting according to the schema.

[Kahncode]

Yes of course, it's less correct. What I'm wondering though is how that will be handled if it was body parameters. As far as I can see in the generated files TSet was not handled at all. This is why I mentioned that going for proper support for sets is a more ambitious change. In this case I'd suggest you test more cases, at least body parameters, and support the TSet fully as it is a valuable improvement.

In any case this is a good change as it is and it looks fine to me.

[wing328]

ci failure not related to this change.

[wing328]

@roseatromero thanks for the PR, which has been merged.

@Kahncode thanks for reviewing the change.

[wing328]

@roseatromero can you please PM me via Slack when you've time next week?

https://join.slack.com/t/openapi-generator/shared_invite/zt-12jxxd7p2-XUeQM~4pzsU9x~eGLQqX2g

Have a nice weekend.