Header lexy/callback/constant.hpp

Callback lexy::constants

lexy/callback/constant.hpp
namespace lexy
{
    template <typename Args>
    consteval callback auto constant(Arg&& arg);
}

Produces a constant value.

It is a callback that accepts zero arguments and produces a copy of the constant.

Example 1. Produce constant values
struct boolean
{
    struct true_
    {
        static constexpr auto rule = LEXY_LIT("true");
        // Produce the value `true`.
        static constexpr auto value = lexy::constant(true);
    };
    struct false_
    {
        static constexpr auto rule = LEXY_LIT("false");
        // Produce the value `false`.
        static constexpr auto value = lexy::constant(false);
    };

    static constexpr auto rule = dsl::p<true_> | dsl::p<false_>;
    // Both rules produce a boolean value, just forward that one.
    static constexpr auto value = lexy::forward<bool>;
};