SDeferred.h

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#ifndef OPAL_SDeferred_HH
#define OPAL_SDeferred_HH
 
// ------------------------------------------------------------------------
// $RCSfile: SDeferred.h,v $
// ------------------------------------------------------------------------
// $Revision: 1.2.4.1 $
// ------------------------------------------------------------------------
// Copyright: see Copyright.readme
// ------------------------------------------------------------------------
//
// Template class: SDeferred<T>
//
// ------------------------------------------------------------------------
//
// $Date: 2004/11/18 22:52:40 $
// $Author: jsberg $
//
// ------------------------------------------------------------------------
 
#include <exception>
#include <iosfwd>
#include <vector>
#include "AbstractObjects/Attribute.h"
#include "AbstractObjects/Expressions.h"
#include "Expressions/SValue.h"
#include "Utilities/LogicalError.h"
#include "Utilities/OpalException.h"
 
namespace Expressions {
 
    // Template class SDeferred
    // ----------------------------------------------------------------------
    //  An deferred expression is always re-evaluated when its value is
    //  required.  This is notably needed to implement random generators.
 
    template <class T>
    class SDeferred : public SValue<T> {
    public:
        //  From scalar expression.
        explicit SDeferred(PtrToScalar<T> expr);
 
        SDeferred(const SDeferred<T>&);
        virtual ~SDeferred();
 
        virtual SDeferred<T>* clone() const;
 
        //  The expression is always re-evaluated.
        virtual T evaluate();
 
        //  Always true.
        virtual bool isExpression() const;
 
        virtual void print(std::ostream&) const;
 
    protected:
        PtrToScalar<T> expr_ptr;
 
    private:
        // Not implemented.
        SDeferred();
        void operator=(const SDeferred<T>&);
 
        // Guard against recursive definition.
        mutable bool in_evaluation;
    };
 
    // Implementation
    // ------------------------------------------------------------------------
 
    template <class T>
    SDeferred<T>::SDeferred(const SDeferred<T>& rhs)
        : SValue<T>(), expr_ptr(rhs.expr_ptr->clone()), in_evaluation(false) {}
 
    template <class T>
    SDeferred<T>::SDeferred(PtrToScalar<T> expr)
        : SValue<T>(), expr_ptr(expr), in_evaluation(false) {}
 
    template <class T>
    SDeferred<T>::~SDeferred() {}
 
    template <class T>
    SDeferred<T>* SDeferred<T>::clone() const {
        return new SDeferred<T>(*this);
    }
 
    template <class T>
    T SDeferred<T>::evaluate() {
        if (in_evaluation) {
            throw LogicalError("SDeferred::evaluate()", "Recursive expression definitions found.");
        } else {
            in_evaluation = true;
            try {
                this->value   = expr_ptr->evaluate();
                in_evaluation = false;
            } catch (OpalException& ex) {
                in_evaluation = false;
                throw LogicalError(
                        ex.where(),
                        "Evaluating expression \"" + this->getImage() + "\": " + ex.what());
            } catch (std::exception& ex) {
                in_evaluation = false;
                throw LogicalError(
                        "SDeferred::evaluate()", "Standard C++ exception while evaluating \""
                                                         + this->getImage() + "\": " + ex.what());
            } catch (...) {
                in_evaluation = false;
                throw LogicalError(
                        "SDeferred::evaluate()",
                        "Unknown exception while evaluating \"" + this->getImage() + "\": ");
            }
        }
 
        return this->value;
    }
 
    template <class T>
    bool SDeferred<T>::isExpression() const {
        return true;
    }
 
    template <class T>
    void SDeferred<T>::print(std::ostream& stream) const {
        expr_ptr->print(stream, 0);
        return;
    }
 
}  // namespace Expressions
 
#endif  // OPAL_SDeferred_HH