/* SPDX-License-Identifier: GPL-2.0 */
/**
 * optional.h - Macros for optional types
 *
 * Copyright (C) 2023 Yaroslav de la Peña Smirnov
 *
 * Poor man's optional "type templates" for C
 */

#ifndef OPTIONAL_H
#define OPTIONAL_H

#include <stdbool.h>

/**
 * OPTIONAL - declare an object that optionally holds type @T
 * @T:		the type of data to hold.
 * @name:	the name of the variable or struct field.
 */
#define OPTIONAL(T, name) struct { bool has; T data; } name

/**
 * OPTNONE - initialize an OPTIONAL object to hold nothing.
 */
#define OPTNONE { .has = false }

/**
 * OPTSOME - initialize an OPTIONAL object to hold something.
 * @d:	data to hold.
 */
#define OPTSOME(d) { .has = true, .data = d }

/**
 * opt_set_none - set an OPTIONAL object to hold nothing.
 * @opt:	OPTIONAL object.
 */
#define opt_set_none(opt) opt.has = false

/**
 * opt_set_some - set an OPTIONAL object to hold something.
 * @opt:	OPTIONAL object.
 * @d:		data to hold.
 */
#define opt_set_some(opt, d) \
	(opt.has = true, opt.data = d)

/**
 * opt_has - true if an OPTIONAL object has something.
 * @opt:	OPTIONAL object.
 */
#define opt_has(opt) (opt.has)

/**
 * opt_hasnt - true if an OPTIONAL object has nothing.
 * @opt:	OPTIONAL object.
 */
#define opt_hasnt(opt) (!opt.has)

/**
 * opt_unwrap - if there's something in @src, copy it to @dst.
 * @src:	OPTIONAL object to copy data of type T from.
 * @dst:	variable of type T to copy to.
 *
 * Returns true if there was something, false if there wasn't.
 */
#define opt_unwrap(src, dst) \
	(opt_has(src) ? (dst = src.data, true) : (false))

/**
 * opt_default - get something from @src or default to @def.
 * @src:	OPTIONAL object to get data from.
 * @def:	default value if there's nothing.
 */
#define opt_default(src, def) opt_has(src) ? src.data : def

#endif