rustyconover opened a new pull request, #562:
URL: https://github.com/apache/datasketches-cpp/pull/562
`density_sketch<T, Kernel, Allocator>` takes an allocator, but a sketch with
anything other than `std::allocator` didn't work, for two reasons:
1. **The kernel only accepted `std::vector<T>`.**
`gaussian_kernel::operator()` took `const std::vector<T>&`, but the sketch
stores its points as `std::vector<T, Allocator>`. Compaction and
`get_estimate()` call the kernel on those points, so the sketch didn't compile:
```
density_sketch_impl.hpp:120:41: error: no match for call to '(const
datasketches::gaussian_kernel<double>) (const std::vector<double,
...test_allocator<double>>&, ...)'
```
The kernel now takes any two vectors of `T`. Existing callers that pass
`std::vector<T>` are unaffected.
2. **An unused member was always default-constructed.** The class had an
`Allocator allocator_` member that neither constructor initialized. That fails
for allocators that require an instance, such as `test_allocator`, whose
default constructor throws for exactly this reason. Nothing reads the member,
and `get_allocator()` already returns the levels' allocator, so this removes it.
### Test
Added `density sketch: custom allocator` to `density_sketch_test.cpp`, using
`test_allocator`. It covers:
- 1,000 updates, which puts the sketch into estimation mode
- `get_estimate`
- merging a second sketch
- a serialize/deserialize round trip with equal estimates
- checking that every byte is released at the end
Without these changes it doesn't compile; with them, all 17 test suites pass
under CTest (GCC 14, aarch64).
We found this in the [DuckDB DataSketches
extension](https://github.com/Query-farm/datasketches). There, aggregate states
keep their sketches in DuckDB's per-query arena through a custom allocator, so
they count toward the memory limit and can spill.
🤖 Generated with [Claude Code](https://claude.com/claude-code)
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