int meta_data_get_double(meta_data_t *md, const char *key, double *value);
int meta_data_get_boolean(meta_data_t *md, const char *key, _Bool *value);
int meta_data_get_double(meta_data_t *md, const char *key, double *value);
int meta_data_get_boolean(meta_data_t *md, const char *key, _Bool *value);