Nullable.h

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#pragma once

#include <string>


enum class NullableInit
{       Valid   };



template< typename ResultType >
struct Nullable
{
    ResultType      Value;
    bool            IsValid;
    std::string     ErrorString;



    Nullable()
        :   IsValid( false )
        ,   Value( ResultType() )
    {}


    explicit Nullable( NullableInit )
        :   IsValid( true )
        ,   Value( ResultType() )
    {}

    Nullable( std::string&& error )
        :   ErrorString( std::move( error ) )
        ,   IsValid( false )
        ,   Value( ResultType() )
    {}

    Nullable( ResultType&& result )
        :   Value( std::move( result ) )
        ,   IsValid( true )
    {}

    Nullable( const Nullable< ResultType >& other )
        :   ErrorString( other.ErrorString )
        ,   IsValid( other.IsValid )
        ,   Value( other.Value )
    {}

    Nullable( Nullable< ResultType >&& other )
        :   ErrorString( std::move( other.ErrorString ) )
        ,   IsValid( other.IsValid )
        ,   Value( std::move( other.Value ) )
    {}

    void operator=( const Nullable< ResultType >& other )
    {
        Value = other.Value;
        IsValid = other.IsValid;
        ErrorString = other.ErrorString;
    }

    void operator=( Nullable< ResultType >&& other )
    {
        Value = std::move( other.Value );
        IsValid = other.IsValid;
        ErrorString = std::move( other.ErrorString );
    }


    bool operator!()
    {
        return !IsValid;
    }

};

#define ReturnIfInvalid( nullable )     if( !nullable.IsValid ) return std::move( nullable.ErrorString );