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harbour-core/harbour/doc/en/objfunc.txt

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/*
* $Id$
*/
/*
* The following parts are Copyright of the individual authors.
* www - http://www.harbour-project.org
*
* Copyright 1999-2000 Chen Kedem <niki@actcom.co.il>
* Documentation for: __objHasData(), __objHasMethod(), __objGetMsgList(),
* __objGetMethodList(), __objGetValueList(),
* __ObjSetValueList(), __objAddMethod(),
* __objAddInline(), __objAddData(), __objModMethod(),
* __objModInline(), __objDelMethod(), __objDelInline(),
* __objDelData(), __objDerivedFrom()
*
* See doc/license.txt for licensing terms.
*
*/
/* $DOC$
* $FUNCNAME$
* __objHasData()
* $CATEGORY$
* Object manipulation
* $ONELINER$
* Determine whether a symbol exist in object as DATA
* $SYNTAX$
* __objHasData( <oObject>, <cSymbol> ) --> lExist
* $ARGUMENTS$
* <oObject> is an object to scan.
*
* <cSymbol> is the name of the symbol to look for.
* $RETURNS$
* __objHasData() return .T. if the given <cSymbol> exist as DATA
* (instance variable) in object <oObject), .F. if it does not exist.
* $DESCRIPTION$
* __objHasData() is a low level class support function that let you
* find out if a symbol is an instance variable in a given object.
* $EXAMPLES$
* oB := TBrowseNew( 0, 0, 24, 79 )
* ? __objHasData( oB, "nLeft" ) // this should return .T.
* ? __objHasData( oB, "lBugFree" ) // hopefully this should be .F.
* ? __objHasData( oB, "Left" ) // .F. since this is a METHOD
* </fixed>
* $STATUS$
* R
* $COMPLIANCE$
* __objHasData() is a Harbour extension.
* $FILES$
* Library is rtl
* $SEEALSO$
* __ObjGetMethodList(),__objGetMsgList(),__objHasMethod()
* $END$
*/
/* $DOC$
* $FUNCNAME$
* __objHasMethod()
* $CATEGORY$
* Object manipulation
* $ONELINER$
* Determine whether a symbol exist in object as METHOD
* $SYNTAX$
* __objHasMethod( <oObject>, <cSymbol> ) --> lExist
* $ARGUMENTS$
* <oObject> is an object to scan.
*
* <cSymbol> is the name of the symbol to look for.
* $RETURNS$
* __objHasMethod() return .T. if the given <cSymbol> exist as METHOD
* (class function) in object <oObject), .F. if it does not exist.
* $DESCRIPTION$
* __objHasMethod() is a low level class support function that let you
* find out if a symbol is a class function in a given object.
* $EXAMPLES$
* oB := TBrowseNew( 0, 0, 24, 79 )
* ? __objHasMethod( oB, "nLeft" ) // .F. since this is a DATA
* ? __objHasMethod( oB, "FixBugs" ) // hopefully this should be .F.
* ? __objHasMethod( oB, "Left" ) // this should return .T.
* </fixed>
* $STATUS$
* R
* $COMPLIANCE$
* __objHasMethod() is a Harbour extension.
* $FILES$
* Library is rtl
* $SEEALSO$
* __ObjGetMethodList(),__objGetMsgList(),__objHasData()
* $END$
*/
/* $DOC$
* $FUNCNAME$
* __objGetMsgList()
* $CATEGORY$
* Object manipulation
* $ONELINER$
* Return names of all DATA or METHOD for a given object
* $SYNTAX$
* __objGetMsgList( <oObject>, [<lData>], [nClassType] ) --> aNames
* $ARGUMENTS$
* <oObject> is an object to scan.
*
* <lData> is an optional logical value that specifies the information
* to return. A value of .T. instruct the function to return list of
* all DATA names, .F. return list of all METHOD names. Default value
* is .T.
*
* <nClassType> is on optional numeric code for selecting which class
* type to return. Default value is HB_MSGLISTALL, returning the whole
* list.
* $RETURNS$
* __objGetMsgList() return an array of character stings with all DATA
* names or all METHOD names for a given object. __objGetMsgList()
* would return an empty array {} if the given object does not contain
* the requested information.
* $DESCRIPTION$
* __objGetMsgList() is a low level class support function that let you
* find all instance variable or method names for a given object.
*
* If specified, the following table shoes the values for <nClassType>
* that allow you to distinguish between DATA and CLASSDATA:
*
* <table>
* hboo.ch Value Meaning
*
* HB_MSGLISTALL 0 All types
* HB_MSGLISTCLASS 1 CLASSDATA only
* HB_MSGLISTPURE 2 DATA only
* </table>
*
* DATA are instance variable usable within each object from a class,
* where each object has its own DATAs.
*
* CLASSDATA are shared by all objects from a Class, so the changed
* value within Object1 will be reflected when accessing the CLASSDATA
* from Object2.
* $EXAMPLES$
* // show information about TBrowse class
* oB := TBrowseNew( 0, 0, 24, 79 )
* aData := __objGetMsgList( oB, .T. )
* aClassData := __objGetMsgList( oB, .T., HB_MSGLISTCLASS )
* aMethod := __objGetMsgList( oB, .F. )
* FOR i = 1 to len ( aData )
* ? "DATA name:", aData[ i ]
* NEXT
* FOR i = 1 to len ( aClassData )
* ? "CLASSDATA name:", aClassData[ i ]
* NEXT
* FOR i = 1 to len ( aMethod )
* ? "METHOD name:", aMethod[ i ]
* NEXT
* </fixed>
* $STATUS$
* R
* $COMPLIANCE$
* __objGetMsgList() is a Harbour extension.
* $FILES$
* Header file is hboo.ch
* Library is rtl
* $SEEALSO$
* __ObjGetMethodList(),__ObjGetValueList(),__objHasData(),__objHasMethod()
* $END$
*/
/* $DOC$
* $FUNCNAME$
* __objGetMethodList()
* $CATEGORY$
* Object manipulation
* $ONELINER$
* Return names of all METHOD for a given object
* $SYNTAX$
* __objGetMethodList( <oObject> ) --> aMethodNames
* $ARGUMENTS$
* <oObject> is an object to scan.
* $RETURNS$
* __objGetMethodList() return an array of character stings with all
* METHOD names for a given object. __objGetMethodList() would return
* an empty array {} if the given object does not contain any METHOD.
* $DESCRIPTION$
* __objGetMethodList() is a low level class support function that let
* you find all class functions names for a given object.
* It is equivalent to __objGetMsgList( oObject, .F. ).
* $EXAMPLES$
* // show information about TBrowse class
* oB := TBrowseNew( 0, 0, 24, 79 )
* aMethod := __objGetMethodList( oB )
* FOR i = 1 to len ( aMethod )
* ? "METHOD name:", aMethod[ i ]
* NEXT
* </fixed>
* $STATUS$
* R
* $COMPLIANCE$
* __objGetMethodList() is a Harbour extension.
* $FILES$
* Library is rtl
* $SEEALSO$
* __objGetMsgList(),__ObjGetValueList(),__objHasData(),__objHasMethod()
* $END$
*/
/* $DOC$
* $FUNCNAME$
* __objGetValueList()
* $CATEGORY$
* Object manipulation
* $ONELINER$
* Return an array of DATA names and values for a given object
* $SYNTAX$
* __objGetValueList( <oObject>, [<aExcept>] ) --> aData
* $ARGUMENTS$
* <oObject> is an object to scan.
*
* <aExcept> is an optional array with DATA names you want to exclude
* from the scan.
* $RETURNS$
* __objGetValueList() return a 2D array that contain pairs of a DATA
* symbol name and the value of DATA. __objGetValueList() would return
* an empty array {} if the given object does not contain the requested
* information.
* $DESCRIPTION$
* __objGetValueList() is a low level class support function that
* return an array with DATA names and value, each array element is a
* pair of: aData[ i, HB_OO_DATA_SYMBOL ] contain the symbol name
* aData[ i, HB_OO_DATA_VALUE ] contain the value of DATA
* $EXAMPLES$
* // show information about TBrowse class
* oB := TBrowseNew( 0, 0, 24, 79 )
* aData := __objGetValueList( oB )
* FOR i = 1 to len ( aData )
* ? "DATA name:", aData[ i, HB_OO_DATA_SYMBOL ], ;
* " value=", aData[ i, HB_OO_DATA_VALUE ]
* NEXT
* </fixed>
* $STATUS$
* R
* $COMPLIANCE$
* __objGetValueList() is a Harbour extension.
* $FILES$
* Header file is hboo.ch
* Library is rtl
* $SEEALSO$
* __objGetMethodList(),__objGetMsgList(),__objHasData(),__objHasMethod(),__ObjSetValueList()
* $END$
*/
/* $DOC$
* $FUNCNAME$
* __ObjSetValueList()
* $CATEGORY$
* Object manipulation
* $ONELINER$
* Set object with an array of DATA names and values
* $SYNTAX$
* __ObjSetValueList( <oObject>, <aData> ) --> oObject
* $ARGUMENTS$
* <oObject> is an object to set.
*
* <aData> is a 2D array with a pair of instance variables and values
* for setting those variable.
* $RETURNS$
* __ObjSetValueList() return a reference to <oObject>.
* $DESCRIPTION$
* __ObjSetValueList() is a low level class support function that let
* you set a group of instance variables with values. each array
* element in <aData> is a pair of:
* aData[ i, HB_OO_DATA_SYMBOL ] which contain the variable name to set
* aData[ i, HB_OO_DATA_VALUE ] contain the new variable value.
* $EXAMPLES$
* // set some TBrowse instance variable
* oB := TBrowse():New()
* aData := array( 4, 2 )
* aData[ 1, HB_OO_DATA_SYMBOL ] = "nTop"
* aData[ 1, HB_OO_DATA_VALUE ] = 1
* aData[ 2, HB_OO_DATA_SYMBOL ] = "nLeft"
* aData[ 2, HB_OO_DATA_VALUE ] = 10
* aData[ 3, HB_OO_DATA_SYMBOL ] = "nBottom"
* aData[ 3, HB_OO_DATA_VALUE ] = 20
* aData[ 4, HB_OO_DATA_SYMBOL ] = "nRight"
* aData[ 4, HB_OO_DATA_VALUE ] = 70
* __ObjSetValueList( oB, aData )
* ? oB:nTop // 1
* ? oB:nLeft // 10
* ? oB:nBottom // 20
* ? oB:nRight // 70
* </fixed>
* $STATUS$
* R
* $COMPLIANCE$
* __ObjSetValueList() is a Harbour extension.
* $FILES$
* Header file is hboo.ch
* Library is rtl
* $SEEALSO$
* __ObjGetValueList()
* $END$
*/
/* $DOC$
* $FUNCNAME$
* __objAddMethod()
* $CATEGORY$
* Object manipulation
* $ONELINER$
* Add a METHOD to an already existing class
* $SYNTAX$
* __objAddMethod( <oObject>, <cMethodName>, <nFuncPtr> ) --> oObject
* $ARGUMENTS$
* <oObject> is the object to work on.
*
* <cMethodName> is the symbol name of the new METHOD to add.
*
* <nFuncPtr> is a pointer to a function to associate with the method.
* $RETURNS$
* __objAddMethod() return a reference to <oObject>.
* $DESCRIPTION$
* __objAddMethod() is a low level class support function that add a
* new METHOD to an object. <oObject> is unchanged if a symbol with the
* name <cMethodName> already exist in <oObject>.
*
* Note that <nFuncPtr> is a special pointer to a function that was
* created using the @ operator, see example below.
* $EXAMPLES$
* // create a new THappy class and add a Smile method
* oHappy := HBClass():New( "THappy" )
* __objAddMethod( oHappy, "Smile", @MySmile() )
* ? oHappy:Smile( 1 ) // :)
* ? oHappy:Smile( 2 ) // ;)
* ? oHappy:Smile( 3 ) // *SMILE*
*
* STATIC FUNCTION MySmile( nType )
* LOCAL cSmile
* DO CASE
* CASE nType == 1
* cSmile := ":)"
* CASE nType == 2
* cSmile := ";)"
* CASE nType == 3
* cSmile := "*SMILE*"
* ENDCASE
* RETURN cSmile
* </fixed>
* $STATUS$
* R
* $COMPLIANCE$
* __objAddMethod() is a Harbour extension.
* $FILES$
* Library is rtl
* $SEEALSO$
* __objAddInline(),__objAddData(),__objDelMethod(),__ObjGetMethodList(),__objGetMsgList(),__objHasMethod(),__objModMethod()
* $END$
*/
/* $DOC$
* $FUNCNAME$
* __objAddInline()
* $CATEGORY$
* Object manipulation
* $ONELINER$
* Add an INLINE to an already existing class
* $SYNTAX$
* __objAddInline( <oObject>, <cInlineName>, <bInline> ) --> oObject
* $ARGUMENTS$
* <oObject> is the object to work on.
*
* <cInlineName> is the symbol name of the new INLINE to add.
*
* <bInline> is a code block to associate with the INLINE method.
* $RETURNS$
* __objAddInline() return a reference to <oObject>.
* $DESCRIPTION$
* __objAddInline() is a low level class support function that add a
* new INLINE method to an object. <oObject> is unchanged if a symbol
* with the name <cInlineName> already exist in <oObject>.
* $EXAMPLES$
* // create a new THappy class and add a Smile INLINE method
* oHappy := HBClass():New( "THappy" )
* bInline := { | nType | { ":)", ";)", "*SMILE*" }[ nType ] }
* __objAddInline( oHappy, "Smile", bInline )
* ? oHappy:Smile( 1 ) // :)
* ? oHappy:Smile( 2 ) // ;)
* ? oHappy:Smile( 3 ) // *SMILE*
* </fixed>
* $STATUS$
* R
* $COMPLIANCE$
* __objAddInline() is a Harbour extension.
* $FILES$
* Library is rtl
* $SEEALSO$
* __objAddData(),__objAddMethod(),__objDelInline(),__ObjGetMethodList(),__objGetMsgList(),__objHasMethod() ,__objModInline()
* $END$
*/
/* $DOC$
* $FUNCNAME$
* __objAddData()
* $CATEGORY$
* Object manipulation
* $ONELINER$
* Add a DATA to an already existing class
* $SYNTAX$
* __objAddData( <oObject>, <cDataName> ) --> oObject
* $ARGUMENTS$
* <oObject> is the object to work on.
*
* <cDataName> is the symbol name of the new DATA to add.
* $RETURNS$
* __objAddData() return a reference to <oObject>.
* $DESCRIPTION$
* __objAddData() is a low level class support function that add a new
* DATA to an object. <oObject> is unchanged if a symbol with the name
* <cDataName> already exist in <oObject>.
* $EXAMPLES$
* // create a new THappy class and add a lHappy DATA
* oHappy := HBClass():New( "THappy" )
* __objAddData( oHappy, "lHappy" )
* oHappy:lHappy := .T.
* IF oHappy:lHappy
* ? "Happy, Happy, Joy, Joy !!!"
* ELSE
* ? ":(..."
* ENDIF
* </fixed>
* $STATUS$
* R
* $COMPLIANCE$
* __objAddData() is a Harbour extension.
* $FILES$
* Library is rtl
* $SEEALSO$
* __objAddInline(),__objAddMethod(),__objDelData(),__objGetMsgList(),__ObjGetValueList(),__objHasData(),__ObjSetValueList()
* $END$
*/
/* $DOC$
* $FUNCNAME$
* __objModMethod()
* $CATEGORY$
* Object manipulation
* $ONELINER$
* Modify (replace) a METHOD in an already existing class
* $SYNTAX$
* __objModMethod( <oObject>, <cMethodName>, <nFuncPtr> ) --> oObject
* $ARGUMENTS$
* <oObject> is the object to work on.
*
* <cMethodName> is the symbol name of the METHOD to modify.
*
* <nFuncPtr> is a pointer to a new function to associate with the
* method.
* $RETURNS$
* __objModMethod() return a reference to <oObject>.
* $DESCRIPTION$
* __objModMethod() is a low level class support function that modify
* a METHOD in an object and replace it with a new function. <oObject>
* is unchanged if a symbol with the name <cMethodName> does not exist
* in <oObject>. __objModMethod() is used in inheritance mechanism.
*
* Note that <nFuncPtr> is a special pointer to a function that was
* created using the @ operator, see example below.
* $EXAMPLES$
* // create a new THappy class and add a Smile method
* oHappy := HBClass():New( "THappy" )
* __objAddMethod( oHappy, "Smile", @MySmile() )
* ? oHappy:Smile( 1 ) // :)
* ? oHappy:Smile( 2 ) // ;)
* // replace Smile method with a new function
* __objAddMethod( oHappy, "Smile", @YourSmile() )
* ? oHappy:Smile( 1 ) // *SMILE*
* ? oHappy:Smile( 2 ) // *WINK*
*
* STATIC FUNCTION MySmile( nType )
* LOCAL cSmile
* DO CASE
* CASE nType == 1
* cSmile := ":)"
* CASE nType == 2
* cSmile := ";)"
* ENDCASE
* RETURN cSmile
*
* STATIC FUNCTION YourSmile( nType )
* LOCAL cSmile
* DO CASE
* CASE nType == 1
* cSmile := "*SMILE*"
* CASE nType == 2
* cSmile := "*WINK*"
* ENDCASE
* RETURN cSmile
* </fixed>
* $STATUS$
* R
* $COMPLIANCE$
* __objModMethod() is a Harbour extension.
* $FILES$
* Library is rtl
* $SEEALSO$
* __objAddMethod(),__objDelMethod(),__ObjGetMethodList(),__objGetMsgList(),__objHasMethod()
* $END$
*/
/* $DOC$
* $FUNCNAME$
* __objModInline()
* $CATEGORY$
* Object manipulation
* $ONELINER$
* Modify (replace) an INLINE method in an already existing class
* $SYNTAX$
* __objModInline( <oObject>, <cInlineName>, <bInline> ) --> oObject
* $ARGUMENTS$
* <oObject> is the object to work on.
*
* <cInlineName> is the symbol name of the INLINE method to modify.
*
* <bInline> is a new code block to associate with the INLINE method.
* $RETURNS$
* __objModInline() return a reference to <oObject>.
* $DESCRIPTION$
* __objModInline() is a low level class support function that modify
* an INLINE method in an object and replace it with a new code block.
* <oObject> is unchanged if a symbol with the name <cInlineName> does
* not exist in <oObject>. __objModInline() is used in inheritance
* mechanism.
* $EXAMPLES$
* // create a new THappy class and add a Smile INLINE method
* oHappy := HBClass():New( "THappy" )
* bMyInline := { | nType | { ":)", ";)" }[ nType ] }
* bYourInline := { | nType | { "*SMILE*", "*WINK*" }[ nType ] }
* __objAddInline( oHappy, "Smile", bMyInline )
* ? oHappy:Smile( 1 ) // :)
* ? oHappy:Smile( 2 ) // ;)
* // replace Smile inline method with a new code block
* __objModInline( oHappy, "Smile", bYourInline )
* ? oHappy:Smile( 1 ) // *SMILE*
* ? oHappy:Smile( 2 ) // *WINK*
* </fixed>
* $STATUS$
* R
* $COMPLIANCE$
* __objModInline() is a Harbour extension.
* $FILES$
* Library is rtl
* $SEEALSO$
* __objAddInline(),__objDelInline(),__ObjGetMethodList(),__objGetMsgList(),__objHasMethod()
* $END$
*/
/* $DOC$
* $FUNCNAME$
* __objDelMethod()
* $CATEGORY$
* Object manipulation
* $ONELINER$
* Delete a METHOD from class
* $SYNTAX$
* __objDelMethod( <oObject>, <cSymbol> ) --> oObject
* $ARGUMENTS$
* <oObject> is the object to work on.
*
* <cSymbol> is the symbol name of METHOD or INLINE method to be
* deleted (removed) from the object.
* $RETURNS$
* __objDelMethod() return a reference to <oObject>.
* $DESCRIPTION$
* __objDelMethod() is a low level class support function that delete
* (remove) a METHOD or an INLINE method from an object. <oObject> is
* unchanged if a symbol with the name <cSymbol> does not exist in
* <oObject>.
*
* __objDelInline() is exactly the same as __objDelMethod().
* $EXAMPLES$
* // create a new THappy class and add a Smile method
* oHappy := HBClass():New( "THappy" )
* __objAddMethod( oHappy, "Smile", @MySmile() )
* ? __objHasMethod( oHappy, "Smile" ) // .T.
* // remove Smile method
* __objDelMethod( oHappy, "Smile" )
* ? __objHasMethod( oHappy, "Smile" ) // .F.
*
* STATIC FUNCTION MySmile( nType )
* LOCAL cSmile
* DO CASE
* CASE nType == 1
* cSmile := ":)"
* CASE nType == 2
* cSmile := ";)"
* ENDCASE
* RETURN cSmile
* </fixed>
* $STATUS$
* R
* $COMPLIANCE$
* __objDelMethod() is a Harbour extension.
* $FILES$
* Library is rtl
* $SEEALSO$
* __objAddInline(),__objAddMethod(),__ObjGetMethodList(),__objGetMsgList(),__objHasMethod(),__objModInline(),__objModMethod()
* $END$
*/
/* $DOC$
* $FUNCNAME$
* __objDelInline()
* $CATEGORY$
* Object manipulation
* $ONELINER$
* Delete a METHOD INLINE from class
* $SYNTAX$
* __objDelInline( <oObject>, <cSymbol> ) --> oObject
* $ARGUMENTS$
* <oObject> is the object to work on.
*
* <cSymbol> is the symbol name of METHOD or INLINE method to be
* deleted (removed) from the object.
* $RETURNS$
* __objDelInMethod() return a reference to <oObject>.
* $DESCRIPTION$
* __objDelInMethod() is a low level class support function that delete
* (remove) a METHOD or an INLINE method from an object. <oObject> is
* unchanged if a symbol with the name <cSymbol> does not exist in
* <oObject>.
* $EXAMPLES$
* // create a new THappy class and add a Smile method
* oHappy := HBClass():New( "THappy" )
* __objAddMethod( oHappy, "Smile", @MySmile() )
* ? __objHasMethod( oHappy, "Smile" ) // .T.
* // remove Smile method
* __objDelInMethod( oHappy, "Smile" )
* ? __objHasMethod( oHappy, "Smile" ) // .F.
*
* STATIC FUNCTION MySmile( nType )
* LOCAL cSmile
* DO CASE
* CASE nType == 1
* cSmile := ":)"
* CASE nType == 2
* cSmile := ";)"
* ENDCASE
* RETURN cSmile
* </fixed>
* $STATUS$
* R
* $COMPLIANCE$
* __objDelMethod() is a Harbour extension.
* $FILES$
* Library is rtl
* $SEEALSO$
* __objAddInline(),__objAddMethod(),__ObjGetMethodList(),__objGetMsgList(),__objHasMethod(),__objModInline(),__objModMethod()
* $END$
*/
/* $DOC$
* $FUNCNAME$
* __objDelData()
* $CATEGORY$
* Object manipulation
* $ONELINER$
* Delete a DATA (instance variable) from class
* $SYNTAX$
* __objDelMethod( <oObject>, <cDataName> ) --> oObject
* $ARGUMENTS$
* <oObject> is the object to work on.
*
* <cDataName> is the symbol name of DATA to be deleted (removed) from
* the object.
* $RETURNS$
* __objDelData() return a reference to <oObject>.
* $DESCRIPTION$
* __objDelData() is a low level class support function that delete
* (remove) a DATA from an object. <oObject> is unchanged if a symbol
* with the name <cDataName> does not exist in <oObject>.
* $EXAMPLES$
* // create a new THappy class and add a lHappy DATA
* oHappy := HBClass():New( "THappy" )
* __objAddData( oHappy, "lHappy" )
* ? __objHasData( oHappy, "lHappy" ) // .T.
* // remove lHappy DATA
* __objDelData( oHappy, "lHappy" )
* ? __objHasData( oHappy, "lHappy" ) // .F.
* </fixed>
* $STATUS$
* R
* $COMPLIANCE$
* __objDelData() is a Harbour extension.
* $FILES$
* Library is rtl
* $SEEALSO$
* __objAddData(),__objGetMsgList(),__ObjGetValueList(),__objHasData(),__ObjSetValueList()
* $END$
*/
/* $DOC$
* $FUNCNAME$
* __objDerivedFrom()
* $CATEGORY$
* Object manipulation
* $ONELINER$
* Determine whether a class is derived from another class
* $SYNTAX$
* __objDerivedFrom( <oObject>, <xSuper> ) --> lIsParent
* $ARGUMENTS$
* <oObject> is the object to check.
*
* <xSuper> is the object that may be a parent. <xSuper> can be either
* an Object or a Character string with the class name.
* $RETURNS$
* __objDerivedFrom() return a logical TRUE (.T.) if <oObject> is
* derived from <xSuper>.
* $DESCRIPTION$
* __objDerivedFrom() is a low level class support function that check
* is one class is a super class of the other, or in other words, does
* class <oObject> a child or descendant of <xSuper>.
* $EXAMPLES$
* // Create three classes and check their relations
*
* #include "hbclass.ch"
* FUNCTION main()
* local oSuper, oObject, oDress
* oSuper := TMood():New()
* oObject := THappy():New()
* oDress := TShirt():New()
* ? __objDerivedFrom( oObject, oSuper ) // .T.
* ? __objDerivedFrom( oSuper, oObject ) // .F.
* ? __objDerivedFrom( oObject, oDress ) // .F.
* RETURN NIL
*
* CLASS TMood
* METHOD New() INLINE Self
* ENDCLASS
*
* CLASS THappy FROM TMood
* METHOD Smile() INLINE qout( "*smile*" )
* ENDCLASS
*
* CLASS TShirt
* DATA Color
* DATA Size
* METHOD New() INLINE Self
* ENDCLASS
* </fixed>
* $STATUS$
* R
* $COMPLIANCE$
* __objDerivedFrom() is a Harbour extension.
* $FILES$
* Library is rtl
* $SEEALSO$
* __objHasData(),__ObjHasMethod()
* $END$
*/