cpp-useful-iterators/include/iterator/detail/macro.h

//
//  macro.h
//  iterator
//
//  Created by Sam Jaffe on 4/1/23.
//  Copyright © 2023 Sam Jaffe. All rights reserved.
//

#ifndef _ITERATOR_MACRO_H
#define _ITERATOR_MACRO_H

#define SFINAE(trait, rval)                                                    \
  template <bool _ = true> std::enable_if_t<trait<It> && _, rval>

#define VAL(X) std::declval<X>()
#define DEREF_TYPE(X) decltype(*VAL(X))
#define TYPE(X, EXPR) decltype(VAL(X).EXPR)
#define EXISTS(EXPR) std::void_t<decltype(EXPR)>

#endif