ArgKind

    // Human-readable type name used in invalid-value error messages. Lines
    // up 1:1 with the ArgKind enum; new entries get a label here.
    static const char *arg_kind_label(ArgKind k) {
        switch (k) {
            case ARG_KIND_ZSTR :

    // false on type-mismatch / out-of-range so the caller can emit a
    // "invalid value 'X' for --flag: expected <type>" message.
    static bool store_value(ArgKind kind, void *target, const char *value) {
        switch (kind) {
            case ARG_KIND_ZSTR : {

    // to unsigned-int kinds at registration time; signed counters would
    // give surprising wrap-around semantics for repeated flags.
    static bool count_bump(ArgKind kind, void *target) {
        switch (kind) {
            case ARG_KIND_U8 :

            ARG_KIND_F32,
            ARG_KIND_F64,
        } ArgKind;
    
        ///

        ///
        typedef struct ArgTarget {
            ArgKind kind;
            void   *target;
        } ArgTarget;

            const char *help;       // one-line description for `--help`
            ArgRole     role;
            ArgKind     kind;
            void       *target;
            bool        seen; // set during parse so missing-required can be checked