symbol_or_epsilon.hpp

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#pragma once
 
#include <optional>
 
#include <alib/tuple>
 
#include <core/normalize.hpp>
 
#include <common/DefaultSymbolType.h>
 
#include <exception/CommonException.h>
 
namespace common {
 
template < class SymbolType = DefaultSymbolType >
class symbol_or_epsilon {
    std::optional < SymbolType > m_symbol;
 
public:
    explicit symbol_or_epsilon ( SymbolType symbol ) : m_symbol ( std::move ( symbol ) ) {
    }
 
    explicit symbol_or_epsilon ( ) = default;
 
    const SymbolType & getSymbol ( ) const & {
        if ( ! m_symbol )
            throw exception::CommonException ( "The symbol is epsilon" );
        else
            return m_symbol.value ( );
    }
 
    SymbolType && getSymbol ( ) && {
        if ( ! m_symbol )
            throw exception::CommonException ( "The symbol is epsilon" );
        else
            return std::move ( m_symbol.value ( ) );
    }
 
    bool is_epsilon ( ) const {
        return ! m_symbol;
    }
 
    auto operator <=> ( const symbol_or_epsilon & other ) const {
        return m_symbol <=> other.m_symbol;
    }
 
    bool operator == ( const symbol_or_epsilon & other ) const {
        return m_symbol == other.m_symbol;
    }
 
    auto operator <=> ( const SymbolType & other ) const {
        return m_symbol <=> other;
    }
 
    bool operator == ( const SymbolType & other ) const {
        return m_symbol == other;
    }
 
    symbol_or_epsilon < SymbolType > & operator ++ ( ) {
        ++ m_symbol.value ( );
 
        return *this;
    }
};
 
template < class SymbolType >
ext::ostream & operator << ( ext::ostream & out, const common::symbol_or_epsilon < SymbolType > & symbol ) {
    out << "(symbol_or_epsilon ";
    if ( symbol.is_epsilon ( ) )
        out << "#E";
    else
        out << symbol.getSymbol ( );
    out << ")";
    return out;
}
 
} /* namespace common */