params.tpp

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#include <alpaqa/params/params.hpp>
 
#include <alpaqa/config/config.hpp>
#include <alpaqa/util/demangled-typename.hpp>
 
#include <charconv>
#include <chrono>
#include <concepts>
#include <map>
#include <numeric>
#include <stdexcept>
#include <string_view>
#include <system_error>
#include <tuple>
#include <type_traits>
 
namespace alpaqa::params {
 
using config_t = DefaultConfig;
 
/// Throw a meaningful error when `s.key` is not empty, to indicate that
/// the given type @p T is not of struct type and cannot be indexed into.
template <class T>
void assert_key_empty(ParamString s) {
    if (!s.key.empty())
        throw invalid_param("Type '" + demangled_typename(typeid(T)) +
                            "' cannot be indexed in '" +
                            std::string(s.full_key) + "'");
}
 
/// Throw a meaningful error to indicate that parameters of type @p T are not
/// supported or implemented.
template <class T>
void unsupported_type(T &, [[maybe_unused]] ParamString s) {
    throw invalid_param("Unknown parameter type '" +
                        demangled_typename(typeid(T)) + "' in '" +
                        std::string(s.full_key) + "'");
}
 
template <>
void set_param(bool &b, ParamString s);
 
template <>
void set_param(std::string_view &v, ParamString s);
 
template <>
void set_param(std::string &v, ParamString s);
 
template <class T>
    requires((std::floating_point<T> || std::integral<T>) && !std::is_enum_v<T>)
void set_param(T &f, ParamString s);
 
template <>
void set_param(vec<config_t> &v, ParamString s);
 
template <class Rep, class Period>
void set_param(std::chrono::duration<Rep, Period> &t, ParamString s);
 
/// Return a function that applies @ref set_param to the given attribute of a
/// value of type @p T.
template <class T, class A>
auto param_setter(A T::*attr) {
    return [attr](T &t, ParamString s) { return set_param(t.*attr, s); };
}
 
/// Function wrapper to set attributes of a struct, type-erasing the type of the
/// attribute.
template <class T>
struct param_setter_fun_t {
    template <class A>
    param_setter_fun_t(A T::*attr) : set(param_setter(attr)) {}
    std::function<void(T &, ParamString)> set;
    void operator()(T &t, ParamString s) const { return set(t, s); }
};
 
/// Dictionary that maps struct attribute names to type-erased functions that
/// set those attributes.
template <class T>
using dict_to_struct_table_t =
    std::map<std::string_view, param_setter_fun_t<T>>;
 
/// Specialize this type to define the attribute name to attribute setters
/// dictionaries for a struct type @p T.
template <class T>
struct dict_to_struct_table {};
 
/// Return a string enumerating the possible attribute names for the struct type
/// @p T.
template <class T>
auto possible_keys() {
    const auto &tbl = dict_to_struct_table<T>::table;
    if (tbl.empty())
        return std::string{};
    auto penult       = std::prev(tbl.end());
    auto quote_concat = [](std::string &&a, auto b) {
        return a + "'" + std::string(b.first) + "', ";
    };
    return std::accumulate(tbl.begin(), penult, std::string{}, quote_concat) +
           "'" + std::string(penult->first) + "'";
}
 
/// Use @p s to index into the struct type @p T and overwrite the attribute
/// given by @p s.key.
template <class T>
    requires requires { dict_to_struct_table<T>::table; }
void set_param(T &t, ParamString s) {
    const auto &m         = dict_to_struct_table<T>::table;
    auto [key, remainder] = split_key(s.key);
    auto it               = m.find(key);
    if (it == m.end())
        throw invalid_param("Invalid key '" + std::string(key) +
                            "' for type '" + demangled_typename(typeid(T)) +
                            "' in '" + std::string(s.full_key) +
                            "',\n  possible keys are: " + possible_keys<T>());
    s.key = remainder;
    it->second.set(t, s);
}
 
/// Helper macro to easily specialize @ref alpaqa::params::dict_to_struct_table.
#define PARAMS_TABLE(type_, ...)                                               \
    template <>                                                                \
    struct dict_to_struct_table<type_> {                                       \
        using type = type_;                                                    \
        inline static const dict_to_struct_table_t<type> table{__VA_ARGS__};   \
    }
 
/// Helper macro to easily initialize a
/// @ref alpaqa::params::dict_to_struct_table_t.
#define PARAMS_MEMBER(name)                                                    \
    {                                                                          \
#name, &type::name                                                     \
    }
 
} // namespace alpaqa::params