zero.H

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/*---------------------------------------------------------------------------*\
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  \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
   \\    /   O peration     |
    \\  /    A nd           | www.openfoam.com
     \\/     M anipulation  |
-------------------------------------------------------------------------------
    Copyright (C) 2011-2016 OpenFOAM Foundation
    Copyright (C) 2017-2019 OpenCFD Ltd.
-------------------------------------------------------------------------------
License
    This file is part of OpenFOAM.
 
    OpenFOAM 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.
 
    OpenFOAM 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 OpenFOAM.  If not, see <http://www.gnu.org/licenses/>.
 
Class
    Foam::zero
 
Description
    A class representing the concept of 0 (zero), which can be used to avoid
    manipulating objects that are known to be \em zero at compile-time.
 
SourceFiles
    zero.C
    zeroI.H
 
SeeAlso
    Foam::one
 
\*---------------------------------------------------------------------------*/
 
#ifndef zero_H
#define zero_H
 
#include "label.H"
 
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
 
namespace Foam
{
 
// Forward declarations
class zero;
class Istream;
class Ostream;
 
/*---------------------------------------------------------------------------*\
                            Class zero Declaration
\*---------------------------------------------------------------------------*/
 
class zero
{
public:
    typedef zero value_type;
 
    // Forward declarations
    class null;
 
    //- Null constructible
    constexpr zero() noexcept {}
 
    //- Construct from Istream consumes no content.
    explicit constexpr zero(Istream&) noexcept {}
 
 
    //- Return false (0) for bool
    inline constexpr operator bool() const noexcept
    {
        return false;
    }
 
    //- Return 0 for label
    inline constexpr operator label() const noexcept
    {
        return 0;
    }
 
    //- Return 0 for float
    inline constexpr operator float() const noexcept
    {
        return 0;
    }
 
    //- Return 0 for double
    inline constexpr operator double() const noexcept
    {
        return 0;
    }
};
 
 
/*---------------------------------------------------------------------------*\
                         Class zero::null Declaration
\*---------------------------------------------------------------------------*/
 
//- A zero class with a null output adapter.
class zero::null
:
    public zero
{
public:
    typedef null value_type;
 
    //- A static zero::null for dereferencing as a dummy element
    static null dummy;
 
    //- Null constructible
    constexpr null() noexcept {}
 
    //- Construct from Istream consumes no content.
    explicit constexpr null(Istream&) noexcept {}
};
 
 
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
 
//- Global zero
static constexpr const zero Zero;
 
// IOstream Operators
 
//- Read from Istream consumes no content.
inline constexpr Istream& operator>>(Istream& is, zero&) noexcept
{
    return is;
}
 
//- Write to Ostream emits no content.
inline constexpr Ostream& operator<<(Ostream& os, const zero::null&) noexcept
{
    return os;
}
 
 
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
 
} // End namespace Foam
 
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
 
#include "zeroI.H"
 
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
 
#endif
 
// ************************************************************************* //