C++ extension fails to compile under GCC/libstdc++ (blocks Linux wheels)

[sqr00t]

Summary

The C++ extension does not compile under GCC + libstdc++ (the Linux/manylinux toolchain). It compiles fine under Apple Clang + libc++ (local macOS dev and the macOS CI runner), which is why the failure only shows up on Linux.

This blocks producing Linux wheels (x86_64 and arm64) and blocks any Linux consumer who builds the published sdist from source.

Root cause

In src/shim.hpp, NumericVector both inherits std::vector<double>'s constructors:

using std::vector<double>::vector;                 // brings in vector(size_type, const value_type&, ...)

and declares its own overlapping constructors:

explicit NumericVector(size_t n) : std::vector<double>(n, 0.0) {}
NumericVector(size_t n, double v) : std::vector<double>(n, v) {}

A call like NumericVector(cols, 0.0) (with cols an int, e.g. shim.hpp:186 and :285) is then ambiguous between the inherited vector(size_type, const value_type&) and the custom NumericVector(size_t, double) — both require the same int → size_t conversion. GCC rejects this per the standard; Clang happens to resolve it.

src/shim.hpp:186:43: error: call of overloaded 'NumericVector(int&, double)' is ambiguous

Confirmed reproducible locally with g++-16 and on the ubuntu-latest CI runner (GCC 13). -fpermissive does not fix it (hard error, not a warning). Casting the argument to size_t does not fix it either (the ambiguity is by-value vs const-ref, both exact matches).

Proposed fix (verified on both Clang and GCC)

Remove the two custom constructors that duplicate the inherited ones, keeping the using declaration:

class NumericVector : public std::vector<double> {
public:
    using std::vector<double>::vector;   // provides (), (n), (n, v), init-list, range, copy, move
    NumericVector(const std::vector<double> &v) : std::vector<double>(v) {}
    // removed: explicit NumericVector(size_t n)     — duplicated inherited ctor
    // removed: NumericVector(size_t n, double v)    — the ambiguous one
    ...
};

All existing NumericVector(...) construction sites ((n, value), (vec), ()) are covered by the inherited constructors; nothing uses brace-init, so this is safe. A minimal repro of this exact change compiles cleanly under both clang++ (libc++) and g++-16 (libstdc++).

Acceptance criteria

• src/shim.hpp compiles under GCC (Linux) and Clang (macOS).
• Enable the Linux legs of the publish matrix (remove continue-on-error, switch Linux builds to cibuildwheel/manylinux — see the matrix CI PR).
• Local uv build on macOS still succeeds and behaviour is unchanged.

Context

Deferred out of the matrix-CI work so that C++ source changes are reviewed separately from CI config. The publish workflow currently builds Linux legs as non-blocking (continue-on-error) until this lands.