nix-super/src/libutil/comparator.hh
pennae cc4038d541 use std::tie() for macro-generated operators
as written the comparisons generate copies, even though it looks as
though they shouldn't.

before:

  Time (mean ± σ):      4.396 s ±  0.002 s    [User: 3.894 s, System: 0.501 s]
  Range (min … max):    4.393 s …  4.399 s    10 runs

after:

  Time (mean ± σ):      4.260 s ±  0.003 s    [User: 3.754 s, System: 0.505 s]
  Range (min … max):    4.257 s …  4.266 s    10 runs
2023-12-19 19:32:16 +01:00

77 lines
2.6 KiB
C++

#pragma once
///@file
#define DECLARE_ONE_CMP(PRE, QUAL, COMPARATOR, MY_TYPE) \
PRE bool QUAL operator COMPARATOR(const MY_TYPE & other) const;
#define DECLARE_EQUAL(prefix, qualification, my_type) \
DECLARE_ONE_CMP(prefix, qualification, ==, my_type)
#define DECLARE_LEQ(prefix, qualification, my_type) \
DECLARE_ONE_CMP(prefix, qualification, <, my_type)
#define DECLARE_NEQ(prefix, qualification, my_type) \
DECLARE_ONE_CMP(prefix, qualification, !=, my_type)
#define GENERATE_ONE_CMP(PRE, QUAL, COMPARATOR, MY_TYPE, ...) \
PRE bool QUAL operator COMPARATOR(const MY_TYPE & other) const { \
__VA_OPT__(const MY_TYPE * me = this;) \
auto fields1 = std::tie( __VA_ARGS__ ); \
__VA_OPT__(me = &other;) \
auto fields2 = std::tie( __VA_ARGS__ ); \
return fields1 COMPARATOR fields2; \
}
#define GENERATE_EQUAL(prefix, qualification, my_type, args...) \
GENERATE_ONE_CMP(prefix, qualification, ==, my_type, args)
#define GENERATE_LEQ(prefix, qualification, my_type, args...) \
GENERATE_ONE_CMP(prefix, qualification, <, my_type, args)
#define GENERATE_NEQ(prefix, qualification, my_type, args...) \
GENERATE_ONE_CMP(prefix, qualification, !=, my_type, args)
/**
* Declare comparison methods without defining them.
*/
#define DECLARE_CMP(my_type) \
DECLARE_EQUAL(,,my_type) \
DECLARE_LEQ(,,my_type) \
DECLARE_NEQ(,,my_type)
/**
* @param prefix This is for something before each declaration like
* `template<classname Foo>`.
*
* @param my_type the type are defining operators for.
*/
#define DECLARE_CMP_EXT(prefix, qualification, my_type) \
DECLARE_EQUAL(prefix, qualification, my_type) \
DECLARE_LEQ(prefix, qualification, my_type) \
DECLARE_NEQ(prefix, qualification, my_type)
/**
* Awful hacky generation of the comparison operators by doing a lexicographic
* comparison between the choosen fields.
*
* ```
* GENERATE_CMP(ClassName, me->field1, me->field2, ...)
* ```
*
* will generate comparison operators semantically equivalent to:
*
* ```
* bool operator<(const ClassName& other) {
* return field1 < other.field1 && field2 < other.field2 && ...;
* }
* ```
*/
#define GENERATE_CMP(args...) \
GENERATE_EQUAL(,,args) \
GENERATE_LEQ(,,args) \
GENERATE_NEQ(,,args)
/**
* @param prefix This is for something before each declaration like
* `template<classname Foo>`.
*
* @param my_type the type are defining operators for.
*/
#define GENERATE_CMP_EXT(prefix, my_type, args...) \
GENERATE_EQUAL(prefix, my_type ::, my_type, args) \
GENERATE_LEQ(prefix, my_type ::, my_type, args) \
GENERATE_NEQ(prefix, my_type ::, my_type, args)