nix-super/src/libutil/comparator.hh

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#pragma once
///@file
/**
* 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_ONE_CMP(COMPARATOR, MY_TYPE, FIELDS...) \
bool operator COMPARATOR(const MY_TYPE& other) const { \
const MY_TYPE* me = this; \
auto fields1 = std::make_tuple( FIELDS ); \
me = &other; \
auto fields2 = std::make_tuple( FIELDS ); \
return fields1 COMPARATOR fields2; \
}
#define GENERATE_EQUAL(args...) GENERATE_ONE_CMP(==, args)
#define GENERATE_LEQ(args...) GENERATE_ONE_CMP(<, args)
#define GENERATE_NEQ(args...) GENERATE_ONE_CMP(!=, args)
#define GENERATE_CMP(args...) \
GENERATE_EQUAL(args) \
GENERATE_LEQ(args) \
GENERATE_NEQ(args)