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AutoLoad.h

Go to the documentation of this file.

#ifndef CLASSLIB_AUTO_LOAD_H
# define CLASSLIB_AUTO_LOAD_H

//<<<<<< INCLUDES                                                       >>>>>>

# include "classlib/utils/SharedLibrary.h"
# include "classlib/utils/Error.h"

namespace lat {
//<<<<<< PUBLIC DEFINES                                                 >>>>>>
//<<<<<< PUBLIC CONSTANTS                                               >>>>>>
//<<<<<< PUBLIC TYPES                                                   >>>>>>
//<<<<<< PUBLIC VARIABLES                                               >>>>>>
//<<<<<< PUBLIC FUNCTIONS                                               >>>>>>
//<<<<<< CLASS DECLARATIONS                                             >>>>>>

class AutoLoadLib
{
public:
    AutoLoadLib (const char *libname);
    // implicit copy constructor
    // implicit assignment operator
    // implicit destructor

    bool                        exists (void);
    SharedLibrary               *library (void);
    SharedLibrary::Function     function (const char *symname);
    SharedLibrary::Data         data (const char *symname);

private:
    const char                  *m_libname;
    SharedLibrary               *m_library;
};

class AutoLoadError : public Error
{
public:
    AutoLoadError (const char *lib, const char *sym, Error *next = 0);

    virtual std::string         explainSelf (void) const;
    virtual Error *             clone (void) const;
    virtual void                rethrow (void);

private:
    const char                  *m_libname;
    const char                  *m_symname;
};

template <class Type>
class AutoLoad
{
public:
    AutoLoad (AutoLoadLib &library, const char *symname);
    // implicit copy constructor
    // implicit assignment operator
    // implicit destructor

    bool                exists (void);
    Type &              operator* (void);
    Type *              operator-> (void);

private:
    void                loadme (void);

    AutoLoadLib &       m_library;
    const char          *m_symname;
    Type                *m_symbol;
};

//<<<<<< INLINE PUBLIC FUNCTIONS                                        >>>>>>

// Helper functions to look up a symbol in an auto-load library.  This
// works by function overloading: if "Type" is a data entity, and thus
// "Type *" is automatically convertible to "void *", one function is
// selected, otherwise "Type" must be a function type and we go for the
// other alternative.
template <class Type>
inline Type *
AutoLoadLookup (AutoLoadLib &lib, const char *symbol, void *)
{ return (Type *) lib.data (symbol); }

template <class Type>
inline Type *
AutoLoadLookup (AutoLoadLib &lib, const char *symbol, ...)
{ return (Type *) lib.function (symbol); }

//<<<<<< INLINE MEMBER FUNCTIONS                                        >>>>>>

template <class Type>
inline
AutoLoad<Type>::AutoLoad (AutoLoadLib &library, const char *funcname)
    : m_library (library),
      m_symname (funcname),
      m_symbol (0)
{}

template <class Type>
inline void
AutoLoad<Type>::loadme (void)
{ if (! m_symbol) m_symbol = AutoLoadLookup<Type> (m_library, m_symname, (Type *) 0); }

template <class Type>
inline bool
AutoLoad<Type>::exists (void)
{ try { loadme (); } catch (AutoLoadError &) {} return m_symbol; }

template <class Type>
inline Type &
AutoLoad<Type>::operator* (void)
{ loadme (); return *m_symbol; }

template <class Type>
inline Type *
AutoLoad<Type>::operator-> (void)
{ loadme (); return m_symbol; }

} // namespace lat
#endif // CLASSLIB_AUTO_LOAD_H

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