[RF] Make RooAbsDataHelper::Exec well-formed for an empty parameter pack#22805
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The body of RooAbsDataHelper::Exec used a range-based for loop over a
braced-init-list of the parameter pack:
for (auto &&val : {static_cast<double>(values)...})
With an empty pack this becomes `for (auto &&val : {})`, which is
ill-formed since the element type cannot be deduced from an empty list.
The empty-pack instantiation is required to be well-formed by
RDataFrame: instantiating Book<RInferredType, Helper> (as done when
booking the helper from Python without explicit column types) compiles
the no-columns branch of Book, which instantiates
RAction<Helper, ..., TypeList<>> and with it Exec<>.
This went unnoticed so far because cling's TClingCallFunc happens to
skip the vtable-driven instantiation of the ill-formed virtual
RAction::Run in the never-taken branch. The stricter wrapper
compilation in CppInterOp surfaces the error, which made
rf408_RDataFrameToRooFit.py fail with cppyy on top of CppInterOp.
Use a fold expression instead, which is valid for an empty pack.
🤖 Done with the help of AI.
Test Results 23 files 23 suites 3d 15h 16m 38s ⏱️ For more details on these failures, see this check. Results for commit 59cb661. |
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The body of RooAbsDataHelper::Exec used a range-based for loop over a braced-init-list of the parameter pack:
With an empty pack this becomes
for (auto &&val : {}), which is ill-formed since the element type cannot be deduced from an empty list.The empty-pack instantiation is required to be well-formed by RDataFrame: instantiating Book<RInferredType, Helper> (as done when booking the helper from Python without explicit column types) compiles the no-columns branch of Book, which instantiates
RAction<Helper, ..., TypeList<>> and with it Exec<>.
This went unnoticed so far because cling's TClingCallFunc happens to skip the vtable-driven instantiation of the ill-formed virtual RAction::Run in the never-taken branch. The stricter wrapper compilation in CppInterOp surfaces the error, which made rf408_RDataFrameToRooFit.py fail with cppyy on top of CppInterOp.
Use a fold expression instead, which is valid for an empty pack.
🤖 Done with the help of AI.