valentina/src/libs/vmisc/lambdaconstants.h

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2022-01-29 10:50:13 +01:00
/************************************************************************
**
** @file lambdaconstants.h
** @author Roman Telezhynskyi <dismine(at)gmail.com>
** @date 29 1, 2022
**
** @brief
** @copyright
** This source code is part of the Valentina project, a pattern making
** program, whose allow create and modeling patterns of clothing.
** Copyright (C) 2022 Valentina project
** <https://gitlab.com/smart-pattern/valentina> All Rights Reserved.
**
** Valentina is free software: you can redistribute it and/or modify
** it under the terms of the GNU General Public License as published by
** the Free Software Foundation, either version 3 of the License, or
** (at your option) any later version.
**
** Valentina is distributed in the hope that it will be useful,
** but WITHOUT ANY WARRANTY; without even the implied warranty of
** MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
** GNU General Public License for more details.
**
** You should have received a copy of the GNU General Public License
** along with Valentina. If not, see <http://www.gnu.org/licenses/>.
**
*************************************************************************/
#ifndef LAMBDACONSTANTS_H
#define LAMBDACONSTANTS_H
/*
given a lambda that wants to capture two constants
const auto k1 = 1000;
const auto k2 = 2000;
int v = 0;
auto lambda = [&v, &k1, &k2]() {
v = k1 * k2;
}
Then unfortunately clang will correctly warn about unnecessary captures. And MSVC will fail to compile if you don't
capture.
https://stackoverflow.com/questions/52416362/unused-lambda-capture-warning-when-capture-is-actually-used
An imperfect solution is to declare the lambda using the V_LAMBDA_CONSTANTS macro.
auto lambda = [&v
V_LAMBDA_CONSTANTS(&k1, &k2)
](){
v = k1 * k2;
}
This should work correctly. Most of the time.
NOTE: There is no comma after the final capture variable before the V_LAMBDA_CONSTANTS macro. The macro is variadic and
will work with 1 or more captures.
*/
#ifndef V_LAMBDA_CONSTANTS
#if defined(Q_CC_MSVC)
#define V_LAMBDA_CONSTANTS(...) ,__VA_ARGS__
#else
#define V_LAMBDA_CONSTANTS(...)
#endif
#endif
#endif // LAMBDACONSTANTS_H