/[svn]/linuxsampler/trunk/src/scriptvm/common.h

Diff of /linuxsampler/trunk/src/scriptvm/common.h

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-revision 2889 by schoenebeck,
Mon Apr 25 17:28:23 2016 UTC
+revision 2942 by schoenebeck,
Wed Jul 13 15:51:06 2016 UTC
 Line 553 
 namespace LinuxSampler {
          VMInt8Array() : data(NULL), size(0) {}
      };
+     /** @brief Dynamically executed variable (abstract base class).
+      *
+      * Interface for the implementation of a dynamically generated content of
+      * a built-in script variable. Most built-in variables are simply pointers
+      * to some native location in memory. So when a script reads them, the
+      * memory location is simply read to get the value of the variable. A
+      * dynamic variable however is not simply a memory location. For each access
+      * to a dynamic variable some native code is executed to actually generate
+      * and provide the content (value) of this type of variable.
+      */
+     class VMDynVar : virtual public VMExpr {
+     public:
+         /**
+          * Whether a script may modify the content of this dynamic variable by
+          * assigning a new value to it.
+          *
+          * @see isConstExpr(), assign()
+          */
+         virtual bool isAssignable() const = 0;
+         /**
+          * Returns true in case this dynamic variable can be considered to be a
+          * constant expression. A constant expression will retain the same value
+          * throughout the entire life time of a script and the expression's
+          * constant value may be evaluated already at script parse time, which
+          * may result in performance benefits during script runtime.
+          *
+          * However due to the "dynamic" behavior of dynamic variables, almost
+          * all dynamic variables are probably not constant expressions. That's
+          * why this method returns @c false by default. If you are really sure
+          * that your dynamic variable implementation can be considered a
+          * constant expression then you may override this method and return
+          * @c true instead. Note that when you return @c true here, your
+          * dynamic variable will really just be executed once; and exectly
+          * already when the script is loaded!
+          *
+          * As an example you may implement a "constant" built-in dynamic
+          * variable that checks for a certain operating system feature and
+          * returns the result of that OS feature check as content (value) of
+          * this dynamic variable. Since the respective OS feature might become
+          * available/unavailable after OS updates, software migration, etc. the
+          * OS feature check should at least be performed once each time the
+          * application is launched. And since the OS feature check might take a
+          * certain amount of execution time, it might make sense to only
+          * perform the check if the respective variable name is actually
+          * referenced at all in the script to be loaded. Note that the dynamic
+          * variable will still be evaluated again though if the script is
+          * loaded again. So it is up to you to probably cache the result in the
+          * implementation of your dynamic variable.
+          *
+          * On doubt, please rather consider to use a constant built-in script
+          * variable instead of implementing a "constant" dynamic variable, due
+          * to the runtime overhead a dynamic variable may cause.
+          *
+          * @see isAssignable()
+          */
+         virtual bool isConstExpr() const { return false; }
+         /**
+          * In case this dynamic variable is assignable, the new value (content)
+          * to be assigned to this dynamic variable.
+          *
+          * By default this method does nothing. Override and implement this
+          * method in your subclass in case your dynamic variable allows to
+          * assign a new value by script.
+          *
+          * @param expr - new value to be assigned to this variable
+          */
+         virtual void assign(VMExpr* expr) {}
+     };
+     /** @brief Dynamically executed variable (of integer data type).
+      *
+      * This is the base class for all built-in integer script variables whose
+      * variable content needs to be provided dynamically by executable native
+      * code on each script variable access.
+      */
+     class VMDynIntVar : virtual public VMDynVar, virtual public VMIntExpr {
+     public:
+     };
+     /** @brief Dynamically executed variable (of string data type).
+      *
+      * This is the base class for all built-in string script variables whose
+      * variable content needs to be provided dynamically by executable native
+      * code on each script variable access.
+      */
+     class VMDynStringVar : virtual public VMDynVar, virtual public VMStringExpr {
+     public:
+     };
      /** @brief Provider for built-in script functions and variables.
       *
       * Abstract base class defining the high-level interface for all classes
-Line 587 
 namespace LinuxSampler {
+Line 678 
 namespace LinuxSampler {
           * variables, which never change their value at runtime.
           */
          virtual std::map<String,int> builtInConstIntVariables() = 0;
+         /**
+          * Returns a variable name indexed map of all built-in dynamic variables,
+          * which are not simply data stores, rather each one of them executes
+          * natively to provide or alter the respective script variable data.
+          */
+         virtual std::map<String,VMDynVar*> builtInDynamicVariables() = 0;
      };
      /** @brief Execution state of a virtual machine.

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