cpp-expect/expect.hpp

//
//  require.hpp
//  gameutils
//
//  Created by Sam Jaffe on 8/19/16.
//

#pragma once

#include <stdexcept>

#undef CONCAT2
#define CONCAT2(A, B) A##B
#undef CONCAT
#define CONCAT(A, B) CONCAT2(A, B)

#undef STRING2
#define STRING2(A) #A
#undef STRING
#define STRING(A) STRING2(A)

#undef GET_MACRO_3
#define GET_MACRO_3(_1,_2,_3,NAME,...) NAME

namespace contract {
  template <typename except>
  void _contract_impl(bool expr, std::string const & msg, char const * = "") {
    if ( ! expr ) throw except{ msg };
  }
  
  template <typename except>
  void _contract_impl(bool expr, char const * msg, char const * = "") {
    if ( ! expr ) throw except{ msg };
  }
}

#define  FIRST_ELEMENT( X, ... ) X
#define SECOND_ELEMENT( X, Y, ... ) Y

#define exception_type( ... ) GET_MACRO_3( __VA_ARGS__, SECOND_ELEMENT, FIRST_ELEMENT, FIRST_ELEMENT )( __VA_ARGS__ )

#define IGNORE( ... )

#define  COMMA_FIRST_ELEMENT( X, ... ) , X
#define COMMA_SECOND_ELEMENT( X, Y, ... ) , Y

#define pop_exception( ... ) GET_MACRO_3( "", ##__VA_ARGS__, COMMA_SECOND_ELEMENT, COMMA_FIRST_ELEMENT, IGNORE )( __VA_ARGS__ )

#if defined( __clang__ ) || defined( __GNUC__ )
# define FUNCTION STRING(__PRETTY_FUNCTION__)
#elif defined( _MSC_VER )
# define FUNCTION STRING(__FUNCTION__)
#else
# define FUNCTION "???"
#endif

#define get_default_message( header, expr ) \
  header #expr ". in " FUNCTION "(" __FILE__ ":" STRING( __LINE__ ) ")"

#define get_subs_message( header, bool_expr, rval_expr ) \
  header #bool_expr " [ with _ = " #rval_expr " ]. in " FUNCTION "(" __FILE__ ":" STRING( __LINE__ ) ")"

/*
 * Usage: 
 *  expects( bool-expr )
 *  expects( bool-expr, custom_msg )
 *  expects( bool-expr, error_type, custom_msg )
 */
#define expects( expr, ... ) \
  contract::_contract_impl< exception_type( std::logic_error, ##__VA_ARGS__ ) >( \
    expr pop_exception( __VA_ARGS__ ), \
    get_default_message( "precondition failed: ", expr ) )

/*
 * Usage:
 *  expects_graceful( bool-expr[, rval] )
 *
 *  rval        - The value to return if the expression is false.
 *                Skip rval for a function returning void.
 */
#define expects_graceful( expr, ... ) \
  if ( ! bool(expr) ) { return __VA_ARGS__; }

/*
 * Usage:
 *  ensures( bool-expr )
 *  ensures( bool-expr, custom_msg )
 *  ensures( bool-expr, error_type, custom_msg )
 */
#define ensures( cond, ... ) \
  contract::_contract_impl< exception_type( std::runtime_error, ##__VA_ARGS__ )>( \
    cond pop_exception( __VA_ARGS__ ) , \
    get_default_message( "postcondition failed: ", cond ) )


/**
 * RVO works if expr is an rvalue, but not if it is an
 * lvalue. e.g:
 * return ensures( expression, condition );
 *   will rvo the object (if expression is rvo-able)
 * but
 * return ensures( var, condition );
 *   will not, instead copies
 * By making _ an argument, both options will move
 *
 * Usage:
 *  return_ensures( rval-expr, ensure-expr )
 *  return_ensures( rval-expr, ensure-expr, custom_msg )
 *  return_ensures( rval-expr, ensure-expr, error_type, custom_msg )
 *
 *  rval-expr   - An expression that can be cast to the return type
 *                of the invoking function. Bound to the token '_'.
 *  ensure-expr - A special boolean expression using the token '_'.
 */
#if __cplusplus < 201300
#define return_ensures( expr, cond, ... ) \
  [ & ]( ) { \
    decltype((expr)) _ = expr; \
    contract::_contract_impl< exception_type( std::runtime_error, ##__VA_ARGS__ ) >( \
        cond pop_exception( __VA_ARGS__ ) , \
        get_subs_message( "postcondition failed: ", cond, expr ) ); \
    return _; \
  }( )
#else
#define return_ensures( expr, cond, ... ) \
  [ _ = expr ]( ) { \
    contract::_contract_impl< exception_type( std::runtime_error, ##__VA_ARGS__ ) >( \
        cond pop_exception( __VA_ARGS__ ) , \
        get_subs_message( "postcondition failed: ", cond, expr ) ); \
    return _; \
  }( )
#endif