Help wanted: error C2338: static_assert failed: 'Cannot format an argument. To make type T formattable, provide a formatter<T> specialization.

[chenboshuo]

          > Most likely it is your bug, you are trying to format something that is not formattable. In any case, maintainers can't help without a repro.

I encounter this issue again, and this is my code

std::string debug_int_surf_surf(surf_surf_int* items, std::string name, const double kCurveParamStep) {
    std::string info;
    int id = 0;
    if(!items) {
        return name + ":no intersection\n";
    }
    while(items) {
        switch(items->int_type) {
            case surf_int_type::int_normal:  // 	Normal (usual) intersection.
                info += std::format("{} {} is a normal intersection\n", name, id);
                break;
            case surf_int_type::int_tangent:  // 	Tangent or coincident intersection, with normals in the same direction.
                info += std::format("{} {} is a tangent intersection\n", name, id);
                break;
            case surf_int_type::int_antitangent:  // Tangent or coincident intersection, with normals in opposite direction.
                info += std::format("{} {} is a antitangent intersection\n", name, id);
                break;
        }
        curve* curve = items->cur;
        if(!curve) {
            SPAposition p = items->end_term->term_pos;
            info += std::format("({} {}) point: ({},{},{})\n\tisolate point\n",  //
                                name,
                                id,                  //
                                p.x(), p.y(), p.z()  //
            );
            items = items->next;
            ++id;
            continue;
        }
        SPAinterval range = curve->param_range();
        double t;
        for(t = range.start_pt(); t <= range.end_pt(); t += kCurveParamStep) {
            SPAposition p;
            curve->eval(t, p);
            info += std::format(                              //
              "({} {}) point:({:.10f}, {:.10f}, {:.10f})\n",  //
              name, id, p.x(), p.y(), p.z());
        }
        t = range.end_pt();
        SPAposition p;
        curve->eval(t, p);
        info += std::format(                              //
          "({} {}) point:({:.10f}, {:.10f}, {:.10f})\n",  //
          name, id, p.x(), p.y(), p.z()                   //
        );

        if(name == "ACIS") {
            pcurve* p_curve = items->pcur2;
            if(p_curve) {
                SPAinterval param_range = p_curve->param_range();
                for(double t = param_range.start_pt(); t <= param_range.end_pt(); t += kCurveParamStep) {
                    SPApar_pos p = p_curve->eval_position(t);
                    info += std::format(            //
                      "(ACIS {}) param:({},{})\n",  //
                      id, p.u, p.v);
                }
            }
        }

        ++id;
        items = items->next;
    }
    return info;
}

This code is correct in VS 2019

Originally posted by @chenboshuo in #3860 (comment)

#3860 can't reopen

[frederick-vs-ja]

p.u and p.v are of type SPAparameter, which is implicitly convertible to double.

In short, SPAparameter is not formattable by default and a program-defined std::formatter specialization is needed.

Archaeological records

MSVC STL's historical dispatch mechanism used to accept some forms of implicit conversion to standard floating-point types, so SPAparameter was able to be formatted as double.

PR #3080 added the type checking you encountered and banned formatting unrecognized types.

Finally, the dispatch mechanism was completely rewritten by PR #3745 which implemented LWG-3631.

References

• http://www-isl.ece.arizona.edu/ACIS-docs/HTM/DATA/BASE/BASE/03CL/0016.HTM
• http://www-isl.ece.arizona.edu/ACIS-docs/HTM/DATA/BASE/BASE/03CL/0019.HTM

[chenboshuo]

p.u and p.v are of type SPAparameter, which is implicitly convertible to double.

In short, SPAparameter is not formattable by default and a program-defined std::formatter specialization is needed.

Archaeological records

MSVC STL's historical dispatch mechanism used to accept some forms of implicit conversion to standard floating-point types, so SPAparameter was able to be formatted as double.

PR #3080 added the type checking you encountered and banned formatting unrecognized types.

Finally, the dispatch mechanism was completely rewritten by PR #3745 which implemented LWG-3631.

References

• http://www-isl.ece.arizona.edu/ACIS-docs/HTM/DATA/BASE/BASE/03CL/0016.HTM
• http://www-isl.ece.arizona.edu/ACIS-docs/HTM/DATA/BASE/BASE/03CL/0019.HTM

Thank you for your answer, I use static_cast<double> and it works.