CRuntimeCompiledExpression.h

Go to the documentation of this file.

/* +------------------------------------------------------------------------+
   |                     Mobile Robot Programming Toolkit (MRPT)            |
   |                          http://www.mrpt.org/                          |
   |                                                                        |
   | Copyright (c) 2005-2018, Individual contributors, see AUTHORS file     |
   | See: http://www.mrpt.org/Authors - All rights reserved.                |
   | Released under BSD License. See details in http://www.mrpt.org/License |
   +------------------------------------------------------------------------+ */
#pragma once

#include <mrpt/core/pimpl.h>

#include <map>
#include <string>
#include <memory>
#include "mrpt-expr_export.h"

namespace exprtk {
    template <typename T>
    class expression;
}

namespace mrpt
{
namespace expr
{
/** A wrapper of `exprtk` runtime expression compiler: it takes a string
 * representing an
 * expression (from a simple mathematical formula to a complete program),
 * compiles it
 * and evaluates its result as many times as required. The result will change as
 * the "variables"
 * appearing in the expression (hold and managed by the user of this object)
 * change.
 *
 * Refer to [exprtk documentation](https://github.com/ArashPartow/exprtk) for
 * reference on supported formulas, control flow instructions, etc.
 *
 * This wrapper is provided to reduce the (very large) compilation time and
 * memory required by the original
 * library, at the cost of only exposing the most commonly used part of its API:
 *  - Only expressions returning `double` are supported.
 *  - Variables must be provided via a `std::map` container **or** pointers to
 * user-stored variables.
 *
 * See examples of usage in the [unit test
 * file](https://github.com/MRPT/mrpt/blob/master/libs/base/src/math/CRuntimeCompiledExpression_unittest.cpp).
 *
 * \note (New in MRPT 1.5.0)
 * \ingroup mrpt_base_grp
 */
class MRPT_EXPR_EXPORT CRuntimeCompiledExpression
{
   public:
    /** Default ctor */
    CRuntimeCompiledExpression();
    ~CRuntimeCompiledExpression();

    /** Initializes the object by compiling an expression.
      * \exception std::runtime_error On any syntax error or undefined symbol
     * while compiling the expression. The `e.what()` message describes what is
     * exactly the problem.
      * \sa register_symbol_table()
      */
    void compile(
        /** [in] The expression to be compiled. */
        const std::string& expression,
        /** [in] Map of variables/constants by `name` ->  `value`. The
           references to the values in this map **must** be ensured to be
           valid thoughout all the life of the compiled expression. */
        const std::map<std::string, double>& variables =
            std::map<std::string, double>(),
        /** A descriptive name of this formula, to be used when generating
           error reports via an  exception, if needed */
        const std::string& expr_name_for_error_reporting = std::string());

    /** Can be used **before** calling compile() to register additional
     * variables by means of **pointers** instead of a std::map  */
    void register_symbol_table(
        /** [in] Map of variables/constants by `name` ->  `value`. The
           references to the values in this map **must** be ensured to be
           valid thoughout all the life of the compiled expression. */
        const std::map<std::string, double*>& variables);

    /** Evaluates the current value of the precompiled formula.
      * \exception std::runtime_error If the formula has not been compiled yet.
    */
    double eval() const;

    /** Returns true if compile() was called and ended without errors. */
    bool is_compiled() const;
    /** Returns the original formula passed to compile(), or an empty string if
     * still not compiled. */
    const std::string& get_original_expression() const;

    /** Access raw exprtk expression object. */
    exprtk::expression<double>& get_raw_exprtk_expr();
    /** Access raw exprtk expression object. */
    const exprtk::expression<double>& get_raw_exprtk_expr() const;

   private:
    struct Impl;
    mrpt::pimpl<Impl> m_impl;
};  // End of class def.

}  // End of namespace


}  // End of namespace