Amiga Magazin: Amiga-CD 1996 July/AMIGA_1996_7.BIN/ausgabe_7_96/pd-programmierung/perl5_002bin.lha/man/catp/perlbot.0

Text File | 1996-03-02 | 44KB | 727 lines

PERLBOT(1)     User Contributed Perl Documentation     PERLBOT(1)


NNNNAAAAMMMMEEEE
       perlbot - Bag'o Object Tricks (the BOT)

DDDDEEEESSSSCCCCRRRRIIIIPPPPTTTTIIIIOOOONNNN
       The following collection of tricks and hints is intended
       to whet curious appetites about such things as the use of
       instance variables and the mechanics of object and class
       relationships.  The reader is encouraged to consult
       relevant textbooks for discussion of Object Oriented
       definitions and methodology.  This is not intended as a
       tutorial for object-oriented programming or as a
       comprehensive guide to Perl's object oriented features,
       nor should it be construed as a style guide.

       The Perl motto still holds:  There's more than one way to
       do it.

OOOOOOOO SSSSCCCCAAAALLLLIIIINNNNGGGG TTTTIIIIPPPPSSSS
       1    Do not attempt to verify the type of $$$$sssseeeellllffff.  That'll
            break if the class is inherited, when the type of
            $$$$sssseeeellllffff is valid but its package isn't what you expect.
            See rule 5.

       2    If an object-oriented (OO) or indirect-object (IO)
            syntax was used, then the object is probably the
            correct type and there's no need to become paranoid
            about it.  Perl isn't a paranoid language anyway.  If
            people subvert the OO or IO syntax then they probably
            know what they're doing and you should let them do
            it.  See rule 1.

       3    Use the two-argument form of _b_l_e_s_s_(_).  Let a subclass
            use your constructor.  See the section on _I_N_H_E_R_I_T_I_N_G
            _A _C_O_N_S_T_R_U_C_T_O_R.

       4    The subclass is allowed to know things about its
            immediate superclass, the superclass is allowed to
            know nothing about a subclass.

       5    Don't be trigger happy with inheritance.  A "using",
            "containing", or "delegation" relationship (some sort
            of aggregation, at least) is often more appropriate.
            See the section on _O_B_J_E_C_T _R_E_L_A_T_I_O_N_S_H_I_P_S, the section
            on _U_S_I_N_G _R_E_L_A_T_I_O_N_S_H_I_P _W_I_T_H _S_D_B_M, and the section on
            _D_E_L_E_G_A_T_I_O_N.

       6    The object is the namespace.  Make package globals
            accessible via the object.  This will remove the
            guess work about the symbol's home package.  See the
            section on _C_L_A_S_S _C_O_N_T_E_X_T _A_N_D _T_H_E _O_B_J_E_C_T.

       7    IO syntax is certainly less noisy, but it is also
            prone to ambiguities which can cause difficult-to-
            find bugs.  Allow people to use the sure-thing OO



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PERLBOT(1)     User Contributed Perl Documentation     PERLBOT(1)


            syntax, even if you don't like it.

       8    Do not use function-call syntax on a method.  You're
            going to be bitten someday.  Someone might move that
            method into a superclass and your code will be
            broken.  On top of that you're feeding the paranoia
            in rule 2.

       9    Don't assume you know the home package of a method.
            You're making it difficult for someone to override
            that method.  See the section on _T_H_I_N_K_I_N_G _O_F _C_O_D_E
            _R_E_U_S_E.

IIIINNNNSSSSTTTTAAAANNNNCCCCEEEE VVVVAAAARRRRIIIIAAAABBBBLLLLEEEESSSS
       An anonymous array or anonymous hash can be used to hold
       instance variables.  Named parameters are also
       demonstrated.

               ppppaaaacccckkkkaaaaggggeeee FFFFoooooooo;;;;

               ssssuuuubbbb nnnneeeewwww {{{{
                       mmmmyyyy $$$$ttttyyyyppppeeee ==== sssshhhhiiiifffftttt;;;;
                       mmmmyyyy %%%%ppppaaaarrrraaaammmmssss ==== @@@@____;;;;
                       mmmmyyyy $$$$sssseeeellllffff ==== {{{{}}}};;;;
                       $$$$sssseeeellllffff---->>>>{{{{''''HHHHiiiigggghhhh''''}}}} ==== $$$$ppppaaaarrrraaaammmmssss{{{{''''HHHHiiiigggghhhh''''}}}};;;;
                       $$$$sssseeeellllffff---->>>>{{{{''''LLLLoooowwww''''}}}}  ==== $$$$ppppaaaarrrraaaammmmssss{{{{''''LLLLoooowwww''''}}}};;;;
                       bbbblllleeeessssssss $$$$sssseeeellllffff,,,, $$$$ttttyyyyppppeeee;;;;
               }}}}

               ppppaaaacccckkkkaaaaggggeeee BBBBaaaarrrr;;;;

               ssssuuuubbbb nnnneeeewwww {{{{
                       mmmmyyyy $$$$ttttyyyyppppeeee ==== sssshhhhiiiifffftttt;;;;
                       mmmmyyyy %%%%ppppaaaarrrraaaammmmssss ==== @@@@____;;;;
                       mmmmyyyy $$$$sssseeeellllffff ==== [[[[]]]];;;;
                       $$$$sssseeeellllffff---->>>>[[[[0000]]]] ==== $$$$ppppaaaarrrraaaammmmssss{{{{''''LLLLeeeefffftttt''''}}}};;;;
                       $$$$sssseeeellllffff---->>>>[[[[1111]]]] ==== $$$$ppppaaaarrrraaaammmmssss{{{{''''RRRRiiiigggghhhhtttt''''}}}};;;;
                       bbbblllleeeessssssss $$$$sssseeeellllffff,,,, $$$$ttttyyyyppppeeee;;;;
               }}}}

               ppppaaaacccckkkkaaaaggggeeee mmmmaaaaiiiinnnn;;;;

               $$$$aaaa ==== FFFFoooooooo---->>>>nnnneeeewwww(((( ''''HHHHiiiigggghhhh'''' ====>>>> 44442222,,,, ''''LLLLoooowwww'''' ====>>>> 11111111 ))));;;;
               pppprrrriiiinnnntttt """"HHHHiiiigggghhhh====$$$$aaaa---->>>>{{{{''''HHHHiiiigggghhhh''''}}}}\\\\nnnn"""";;;;
               pppprrrriiiinnnntttt """"LLLLoooowwww====$$$$aaaa---->>>>{{{{''''LLLLoooowwww''''}}}}\\\\nnnn"""";;;;

               $$$$bbbb ==== BBBBaaaarrrr---->>>>nnnneeeewwww(((( ''''LLLLeeeefffftttt'''' ====>>>> 77778888,,,, ''''RRRRiiiigggghhhhtttt'''' ====>>>> 44440000 ))));;;;
               pppprrrriiiinnnntttt """"LLLLeeeefffftttt====$$$$bbbb---->>>>[[[[0000]]]]\\\\nnnn"""";;;;
               pppprrrriiiinnnntttt """"RRRRiiiigggghhhhtttt====$$$$bbbb---->>>>[[[[1111]]]]\\\\nnnn"""";;;;


SSSSCCCCAAAALLLLAAAARRRR IIIINNNNSSSSTTTTAAAANNNNCCCCEEEE VVVVAAAARRRRIIIIAAAABBBBLLLLEEEESSSS
       An anonymous scalar can be used when only one instance
       variable is needed.



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               ppppaaaacccckkkkaaaaggggeeee FFFFoooooooo;;;;

               ssssuuuubbbb nnnneeeewwww {{{{
                       mmmmyyyy $$$$ttttyyyyppppeeee ==== sssshhhhiiiifffftttt;;;;
                       mmmmyyyy $$$$sssseeeellllffff;;;;
                       $$$$sssseeeellllffff ==== sssshhhhiiiifffftttt;;;;
                       bbbblllleeeessssssss \\\\$$$$sssseeeellllffff,,,, $$$$ttttyyyyppppeeee;;;;
               }}}}

               ppppaaaacccckkkkaaaaggggeeee mmmmaaaaiiiinnnn;;;;

               $$$$aaaa ==== FFFFoooooooo---->>>>nnnneeeewwww(((( 44442222 ))));;;;
               pppprrrriiiinnnntttt """"aaaa====$$$$$$$$aaaa\\\\nnnn"""";;;;


IIIINNNNSSSSTTTTAAAANNNNCCCCEEEE VVVVAAAARRRRIIIIAAAABBBBLLLLEEEE IIIINNNNHHHHEEEERRRRIIIITTTTAAAANNNNCCCCEEEE
       This example demonstrates how one might inherit instance
       variables from a superclass for inclusion in the new
       class.  This requires calling the superclass's constructor
       and adding one's own instance variables to the new object.

               ppppaaaacccckkkkaaaaggggeeee BBBBaaaarrrr;;;;

               ssssuuuubbbb nnnneeeewwww {{{{
                       mmmmyyyy $$$$ttttyyyyppppeeee ==== sssshhhhiiiifffftttt;;;;
                       mmmmyyyy $$$$sssseeeellllffff ==== {{{{}}}};;;;
                       $$$$sssseeeellllffff---->>>>{{{{''''bbbbuuuuzzzz''''}}}} ==== 44442222;;;;
                       bbbblllleeeessssssss $$$$sssseeeellllffff,,,, $$$$ttttyyyyppppeeee;;;;
               }}}}

               ppppaaaacccckkkkaaaaggggeeee FFFFoooooooo;;;;
               @@@@IIIISSSSAAAA ==== qqqqwwww(((( BBBBaaaarrrr ))));;;;

               ssssuuuubbbb nnnneeeewwww {{{{
                       mmmmyyyy $$$$ttttyyyyppppeeee ==== sssshhhhiiiifffftttt;;;;
                       mmmmyyyy $$$$sssseeeellllffff ==== BBBBaaaarrrr---->>>>nnnneeeewwww;;;;
                       $$$$sssseeeellllffff---->>>>{{{{''''bbbbiiiizzzz''''}}}} ==== 11111111;;;;
                       bbbblllleeeessssssss $$$$sssseeeellllffff,,,, $$$$ttttyyyyppppeeee;;;;
               }}}}

               ppppaaaacccckkkkaaaaggggeeee mmmmaaaaiiiinnnn;;;;

               $$$$aaaa ==== FFFFoooooooo---->>>>nnnneeeewwww;;;;
               pppprrrriiiinnnntttt """"bbbbuuuuzzzz ==== """",,,, $$$$aaaa---->>>>{{{{''''bbbbuuuuzzzz''''}}}},,,, """"\\\\nnnn"""";;;;
               pppprrrriiiinnnntttt """"bbbbiiiizzzz ==== """",,,, $$$$aaaa---->>>>{{{{''''bbbbiiiizzzz''''}}}},,,, """"\\\\nnnn"""";;;;


OOOOBBBBJJJJEEEECCCCTTTT RRRREEEELLLLAAAATTTTIIIIOOOONNNNSSSSHHHHIIIIPPPPSSSS
       The following demonstrates how one might implement
       "containing" and "using" relationships between objects.

               ppppaaaacccckkkkaaaaggggeeee BBBBaaaarrrr;;;;





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PERLBOT(1)     User Contributed Perl Documentation     PERLBOT(1)


               ssssuuuubbbb nnnneeeewwww {{{{
                       mmmmyyyy $$$$ttttyyyyppppeeee ==== sssshhhhiiiifffftttt;;;;
                       mmmmyyyy $$$$sssseeeellllffff ==== {{{{}}}};;;;
                       $$$$sssseeeellllffff---->>>>{{{{''''bbbbuuuuzzzz''''}}}} ==== 44442222;;;;
                       bbbblllleeeessssssss $$$$sssseeeellllffff,,,, $$$$ttttyyyyppppeeee;;;;
               }}}}

               ppppaaaacccckkkkaaaaggggeeee FFFFoooooooo;;;;

               ssssuuuubbbb nnnneeeewwww {{{{
                       mmmmyyyy $$$$ttttyyyyppppeeee ==== sssshhhhiiiifffftttt;;;;
                       mmmmyyyy $$$$sssseeeellllffff ==== {{{{}}}};;;;
                       $$$$sssseeeellllffff---->>>>{{{{''''BBBBaaaarrrr''''}}}} ==== BBBBaaaarrrr---->>>>nnnneeeewwww;;;;
                       $$$$sssseeeellllffff---->>>>{{{{''''bbbbiiiizzzz''''}}}} ==== 11111111;;;;
                       bbbblllleeeessssssss $$$$sssseeeellllffff,,,, $$$$ttttyyyyppppeeee;;;;
               }}}}

               ppppaaaacccckkkkaaaaggggeeee mmmmaaaaiiiinnnn;;;;

               $$$$aaaa ==== FFFFoooooooo---->>>>nnnneeeewwww;;;;
               pppprrrriiiinnnntttt """"bbbbuuuuzzzz ==== """",,,, $$$$aaaa---->>>>{{{{''''BBBBaaaarrrr''''}}}}---->>>>{{{{''''bbbbuuuuzzzz''''}}}},,,, """"\\\\nnnn"""";;;;
               pppprrrriiiinnnntttt """"bbbbiiiizzzz ==== """",,,, $$$$aaaa---->>>>{{{{''''bbbbiiiizzzz''''}}}},,,, """"\\\\nnnn"""";;;;


OOOOVVVVEEEERRRRRRRRIIIIDDDDIIIINNNNGGGG SSSSUUUUPPPPEEEERRRRCCCCLLLLAAAASSSSSSSS MMMMEEEETTTTHHHHOOOODDDDSSSS
       The following example demonstrates how to override a
       superclass method and then call the overridden method.
       The SSSSUUUUPPPPEEEERRRR pseudo-class allows the programmer to call an
       overridden superclass method without actually knowing
       where that method is defined.

               ppppaaaacccckkkkaaaaggggeeee BBBBuuuuzzzz;;;;
               ssssuuuubbbb ggggoooooooo {{{{ pppprrrriiiinnnntttt """"hhhheeeerrrreeee''''ssss tttthhhheeee ggggoooooooo\\\\nnnn"""" }}}}

               ppppaaaacccckkkkaaaaggggeeee BBBBaaaarrrr;;;; @@@@IIIISSSSAAAA ==== qqqqwwww(((( BBBBuuuuzzzz ))));;;;
               ssssuuuubbbb ggggoooooooogggglllleeee {{{{ pppprrrriiiinnnntttt """"ggggoooooooogggglllleeee hhhheeeerrrreeee\\\\nnnn"""" }}}}

               ppppaaaacccckkkkaaaaggggeeee BBBBaaaazzzz;;;;
               ssssuuuubbbb mmmmuuuummmmbbbblllleeee {{{{ pppprrrriiiinnnntttt """"mmmmuuuummmmbbbblllliiiinnnngggg\\\\nnnn"""" }}}}

               ppppaaaacccckkkkaaaaggggeeee FFFFoooooooo;;;;
               @@@@IIIISSSSAAAA ==== qqqqwwww(((( BBBBaaaarrrr BBBBaaaazzzz ))));;;;















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               ssssuuuubbbb nnnneeeewwww {{{{
                       mmmmyyyy $$$$ttttyyyyppppeeee ==== sssshhhhiiiifffftttt;;;;
                       bbbblllleeeessssssss [[[[]]]],,,, $$$$ttttyyyyppppeeee;;;;
               }}}}
               ssssuuuubbbb ggggrrrrrrrr {{{{ pppprrrriiiinnnntttt """"ggggrrrruuuummmmbbbblllleeee\\\\nnnn"""" }}}}
               ssssuuuubbbb ggggoooooooo {{{{
                       mmmmyyyy $$$$sssseeeellllffff ==== sssshhhhiiiifffftttt;;;;
                       $$$$sssseeeellllffff---->>>>SSSSUUUUPPPPEEEERRRR::::::::ggggoooooooo(((())));;;;
               }}}}
               ssssuuuubbbb mmmmuuuummmmbbbblllleeee {{{{
                       mmmmyyyy $$$$sssseeeellllffff ==== sssshhhhiiiifffftttt;;;;
                       $$$$sssseeeellllffff---->>>>SSSSUUUUPPPPEEEERRRR::::::::mmmmuuuummmmbbbblllleeee(((())));;;;
               }}}}
               ssssuuuubbbb ggggoooooooogggglllleeee {{{{
                       mmmmyyyy $$$$sssseeeellllffff ==== sssshhhhiiiifffftttt;;;;
                       $$$$sssseeeellllffff---->>>>SSSSUUUUPPPPEEEERRRR::::::::ggggoooooooogggglllleeee(((())));;;;
               }}}}

               ppppaaaacccckkkkaaaaggggeeee mmmmaaaaiiiinnnn;;;;

               $$$$ffffoooooooo ==== FFFFoooooooo---->>>>nnnneeeewwww;;;;
               $$$$ffffoooooooo---->>>>mmmmuuuummmmbbbblllleeee;;;;
               $$$$ffffoooooooo---->>>>ggggrrrrrrrr;;;;
               $$$$ffffoooooooo---->>>>ggggoooooooo;;;;
               $$$$ffffoooooooo---->>>>ggggoooooooogggglllleeee;;;;


UUUUSSSSIIIINNNNGGGG RRRREEEELLLLAAAATTTTIIIIOOOONNNNSSSSHHHHIIIIPPPP WWWWIIIITTTTHHHH SSSSDDDDBBBBMMMM
       This example demonstrates an interface for the SDBM class.
       This creates a "using" relationship between the SDBM class
       and the new class Mydbm.

               ppppaaaacccckkkkaaaaggggeeee MMMMyyyyddddbbbbmmmm;;;;

               rrrreeeeqqqquuuuiiiirrrreeee SSSSDDDDBBBBMMMM____FFFFiiiilllleeee;;;;
               rrrreeeeqqqquuuuiiiirrrreeee TTTTiiiieeee::::::::HHHHaaaasssshhhh;;;;
               @@@@IIIISSSSAAAA ==== qqqqwwww(((( TTTTiiiieeee::::::::HHHHaaaasssshhhh ))));;;;




















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PERLBOT(1)     User Contributed Perl Documentation     PERLBOT(1)


               ssssuuuubbbb TTTTIIIIEEEEHHHHAAAASSSSHHHH {{{{
                   mmmmyyyy $$$$ttttyyyyppppeeee ==== sssshhhhiiiifffftttt;;;;
                   mmmmyyyy $$$$rrrreeeeffff  ==== SSSSDDDDBBBBMMMM____FFFFiiiilllleeee---->>>>nnnneeeewwww((((@@@@____))));;;;
                   bbbblllleeeessssssss {{{{''''ddddbbbbmmmm'''' ====>>>> $$$$rrrreeeeffff}}}},,,, $$$$ttttyyyyppppeeee;;;;
               }}}}
               ssssuuuubbbb FFFFEEEETTTTCCCCHHHH {{{{
                   mmmmyyyy $$$$sssseeeellllffff ==== sssshhhhiiiifffftttt;;;;
                   mmmmyyyy $$$$rrrreeeeffff  ==== $$$$sssseeeellllffff---->>>>{{{{''''ddddbbbbmmmm''''}}}};;;;
                   $$$$rrrreeeeffff---->>>>FFFFEEEETTTTCCCCHHHH((((@@@@____))));;;;
               }}}}
               ssssuuuubbbb SSSSTTTTOOOORRRREEEE {{{{
                   mmmmyyyy $$$$sssseeeellllffff ==== sssshhhhiiiifffftttt;;;;
                   iiiiffff ((((ddddeeeeffffiiiinnnneeeedddd $$$$____[[[[0000]]]])))){{{{
                       mmmmyyyy $$$$rrrreeeeffff ==== $$$$sssseeeellllffff---->>>>{{{{''''ddddbbbbmmmm''''}}}};;;;
                       $$$$rrrreeeeffff---->>>>SSSSTTTTOOOORRRREEEE((((@@@@____))));;;;
                   }}}} eeeellllsssseeee {{{{
                       ddddiiiieeee """"CCCCaaaannnnnnnnooootttt SSSSTTTTOOOORRRREEEE aaaannnn uuuunnnnddddeeeeffffiiiinnnneeeedddd kkkkeeeeyyyy iiiinnnn MMMMyyyyddddbbbbmmmm\\\\nnnn"""";;;;
                   }}}}
               }}}}

               ppppaaaacccckkkkaaaaggggeeee mmmmaaaaiiiinnnn;;;;
               uuuusssseeee FFFFccccnnnnttttllll qqqqwwww(((( OOOO____RRRRDDDDWWWWRRRR OOOO____CCCCRRRREEEEAAAATTTT ))));;;;

               ttttiiiieeee %%%%ffffoooooooo,,,, MMMMyyyyddddbbbbmmmm,,,, """"SSSSddddbbbbmmmm"""",,,, OOOO____RRRRDDDDWWWWRRRR||||OOOO____CCCCRRRREEEEAAAATTTT,,,, 0000666644440000;;;;
               $$$$ffffoooooooo{{{{''''bbbbaaaarrrr''''}}}} ==== 111122223333;;;;
               pppprrrriiiinnnntttt """"ffffoooooooo----bbbbaaaarrrr ==== $$$$ffffoooooooo{{{{''''bbbbaaaarrrr''''}}}}\\\\nnnn"""";;;;

               ttttiiiieeee %%%%bbbbaaaarrrr,,,, MMMMyyyyddddbbbbmmmm,,,, """"SSSSddddbbbbmmmm2222"""",,,, OOOO____RRRRDDDDWWWWRRRR||||OOOO____CCCCRRRREEEEAAAATTTT,,,, 0000666644440000;;;;
               $$$$bbbbaaaarrrr{{{{''''CCCCaaaatttthhhhyyyy''''}}}} ==== 444455556666;;;;
               pppprrrriiiinnnntttt """"bbbbaaaarrrr----CCCCaaaatttthhhhyyyy ==== $$$$bbbbaaaarrrr{{{{''''CCCCaaaatttthhhhyyyy''''}}}}\\\\nnnn"""";;;;


TTTTHHHHIIIINNNNKKKKIIIINNNNGGGG OOOOFFFF CCCCOOOODDDDEEEE RRRREEEEUUUUSSSSEEEE
       One strength of Object-Oriented languages is the ease with
       which old code can use new code.  The following examples
       will demonstrate first how one can hinder code reuse and
       then how one can promote code reuse.

       This first example illustrates a class which uses a fully-
       qualified method call to access the "private" method
       _B_A_Z_(_).  The second example will show that it is impossible
       to override the _B_A_Z_(_) method.

               ppppaaaacccckkkkaaaaggggeeee FFFFOOOOOOOO;;;;

               ssssuuuubbbb nnnneeeewwww {{{{
                       mmmmyyyy $$$$ttttyyyyppppeeee ==== sssshhhhiiiifffftttt;;;;
                       bbbblllleeeessssssss {{{{}}}},,,, $$$$ttttyyyyppppeeee;;;;
               }}}}
               ssssuuuubbbb bbbbaaaarrrr {{{{
                       mmmmyyyy $$$$sssseeeellllffff ==== sssshhhhiiiifffftttt;;;;
                       $$$$sssseeeellllffff---->>>>FFFFOOOOOOOO::::::::pppprrrriiiivvvvaaaatttteeee::::::::BBBBAAAAZZZZ;;;;
               }}}}




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               ppppaaaacccckkkkaaaaggggeeee FFFFOOOOOOOO::::::::pppprrrriiiivvvvaaaatttteeee;;;;

               ssssuuuubbbb BBBBAAAAZZZZ {{{{
                       pppprrrriiiinnnntttt """"iiiinnnn BBBBAAAAZZZZ\\\\nnnn"""";;;;
               }}}}

               ppppaaaacccckkkkaaaaggggeeee mmmmaaaaiiiinnnn;;;;

               $$$$aaaa ==== FFFFOOOOOOOO---->>>>nnnneeeewwww;;;;
               $$$$aaaa---->>>>bbbbaaaarrrr;;;;

       Now we try to override the _B_A_Z_(_) method.  We would like
       _F_O_O_:_:_b_a_r_(_) to call _G_O_O_P_:_:_B_A_Z_(_), but this cannot happen
       because _F_O_O_:_:_b_a_r_(_) explicitly calls _F_O_O_:_:_p_r_i_v_a_t_e_:_:_B_A_Z_(_).

               ppppaaaacccckkkkaaaaggggeeee FFFFOOOOOOOO;;;;

               ssssuuuubbbb nnnneeeewwww {{{{
                       mmmmyyyy $$$$ttttyyyyppppeeee ==== sssshhhhiiiifffftttt;;;;
                       bbbblllleeeessssssss {{{{}}}},,,, $$$$ttttyyyyppppeeee;;;;
               }}}}
               ssssuuuubbbb bbbbaaaarrrr {{{{
                       mmmmyyyy $$$$sssseeeellllffff ==== sssshhhhiiiifffftttt;;;;
                       $$$$sssseeeellllffff---->>>>FFFFOOOOOOOO::::::::pppprrrriiiivvvvaaaatttteeee::::::::BBBBAAAAZZZZ;;;;
               }}}}

               ppppaaaacccckkkkaaaaggggeeee FFFFOOOOOOOO::::::::pppprrrriiiivvvvaaaatttteeee;;;;

               ssssuuuubbbb BBBBAAAAZZZZ {{{{
                       pppprrrriiiinnnntttt """"iiiinnnn BBBBAAAAZZZZ\\\\nnnn"""";;;;
               }}}}

               ppppaaaacccckkkkaaaaggggeeee GGGGOOOOOOOOPPPP;;;;
               @@@@IIIISSSSAAAA ==== qqqqwwww(((( FFFFOOOOOOOO ))));;;;
               ssssuuuubbbb nnnneeeewwww {{{{
                       mmmmyyyy $$$$ttttyyyyppppeeee ==== sssshhhhiiiifffftttt;;;;
                       bbbblllleeeessssssss {{{{}}}},,,, $$$$ttttyyyyppppeeee;;;;
               }}}}

               ssssuuuubbbb BBBBAAAAZZZZ {{{{
                       pppprrrriiiinnnntttt """"iiiinnnn GGGGOOOOOOOOPPPP::::::::BBBBAAAAZZZZ\\\\nnnn"""";;;;
               }}}}

               ppppaaaacccckkkkaaaaggggeeee mmmmaaaaiiiinnnn;;;;

               $$$$aaaa ==== GGGGOOOOOOOOPPPP---->>>>nnnneeeewwww;;;;
               $$$$aaaa---->>>>bbbbaaaarrrr;;;;

       To create reusable code we must modify class FOO,
       flattening class FOO::private.  The next example shows a
       reusable class FOO which allows the method _G_O_O_P_:_:_B_A_Z_(_) to
       be used in place of _F_O_O_:_:_B_A_Z_(_).

               ppppaaaacccckkkkaaaaggggeeee FFFFOOOOOOOO;;;;



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               ssssuuuubbbb nnnneeeewwww {{{{
                       mmmmyyyy $$$$ttttyyyyppppeeee ==== sssshhhhiiiifffftttt;;;;
                       bbbblllleeeessssssss {{{{}}}},,,, $$$$ttttyyyyppppeeee;;;;
               }}}}
               ssssuuuubbbb bbbbaaaarrrr {{{{
                       mmmmyyyy $$$$sssseeeellllffff ==== sssshhhhiiiifffftttt;;;;
                       $$$$sssseeeellllffff---->>>>BBBBAAAAZZZZ;;;;
               }}}}

               ssssuuuubbbb BBBBAAAAZZZZ {{{{
                       pppprrrriiiinnnntttt """"iiiinnnn BBBBAAAAZZZZ\\\\nnnn"""";;;;
               }}}}

               ppppaaaacccckkkkaaaaggggeeee GGGGOOOOOOOOPPPP;;;;
               @@@@IIIISSSSAAAA ==== qqqqwwww(((( FFFFOOOOOOOO ))));;;;

               ssssuuuubbbb nnnneeeewwww {{{{
                       mmmmyyyy $$$$ttttyyyyppppeeee ==== sssshhhhiiiifffftttt;;;;
                       bbbblllleeeessssssss {{{{}}}},,,, $$$$ttttyyyyppppeeee;;;;
               }}}}
               ssssuuuubbbb BBBBAAAAZZZZ {{{{
                       pppprrrriiiinnnntttt """"iiiinnnn GGGGOOOOOOOOPPPP::::::::BBBBAAAAZZZZ\\\\nnnn"""";;;;
               }}}}

               ppppaaaacccckkkkaaaaggggeeee mmmmaaaaiiiinnnn;;;;

               $$$$aaaa ==== GGGGOOOOOOOOPPPP---->>>>nnnneeeewwww;;;;
               $$$$aaaa---->>>>bbbbaaaarrrr;;;;


CCCCLLLLAAAASSSSSSSS CCCCOOOONNNNTTTTEEEEXXXXTTTT AAAANNNNDDDD TTTTHHHHEEEE OOOOBBBBJJJJEEEECCCCTTTT
       Use the object to solve package and class context
       problems.  Everything a method needs should be available
       via the object or should be passed as a parameter to the
       method.

       A class will sometimes have static or global data to be
       used by the methods.  A subclass may want to override that
       data and replace it with new data.  When this happens the
       superclass may not know how to find the new copy of the
       data.

       This problem can be solved by using the object to define
       the context of the method.  Let the method look in the
       object for a reference to the data.  The alternative is to
       force the method to go hunting for the data ("Is it in my
       class, or in a subclass?  Which subclass?"), and this can
       be inconvenient and will lead to hackery.  It is better to
       just let the object tell the method where that data is
       located.

               ppppaaaacccckkkkaaaaggggeeee BBBBaaaarrrr;;;;

               %%%%ffffiiiizzzzzzzzlllleeee ==== (((( ''''PPPPaaaasssssssswwwwoooorrrrdddd'''' ====>>>> ''''XXXXYYYYZZZZZZZZYYYY'''' ))));;;;



12/Feb/96                perl 5.002 with                        8





PERLBOT(1)     User Contributed Perl Documentation     PERLBOT(1)


               ssssuuuubbbb nnnneeeewwww {{{{
                       mmmmyyyy $$$$ttttyyyyppppeeee ==== sssshhhhiiiifffftttt;;;;
                       mmmmyyyy $$$$sssseeeellllffff ==== {{{{}}}};;;;
                       $$$$sssseeeellllffff---->>>>{{{{''''ffffiiiizzzzzzzzlllleeee''''}}}} ==== \\\\%%%%ffffiiiizzzzzzzzlllleeee;;;;
                       bbbblllleeeessssssss $$$$sssseeeellllffff,,,, $$$$ttttyyyyppppeeee;;;;
               }}}}

               ssssuuuubbbb eeeennnntttteeeerrrr {{{{
                       mmmmyyyy $$$$sssseeeellllffff ==== sssshhhhiiiifffftttt;;;;

                       #### DDDDoooonnnn''''tttt ttttrrrryyyy ttttoooo gggguuuueeeessssssss iiiiffff wwwweeee sssshhhhoooouuuulllldddd uuuusssseeee %%%%BBBBaaaarrrr::::::::ffffiiiizzzzzzzzlllleeee
                       #### oooorrrr %%%%FFFFoooooooo::::::::ffffiiiizzzzzzzzlllleeee....  TTTThhhheeee oooobbbbjjjjeeeecccctttt aaaallllrrrreeeeaaaaddddyyyy kkkknnnnoooowwwwssss wwwwhhhhiiiicccchhhh
                       #### wwwweeee sssshhhhoooouuuulllldddd uuuusssseeee,,,, ssssoooo jjjjuuuusssstttt aaaasssskkkk iiiitttt....
                       ####
                       mmmmyyyy $$$$ffffiiiizzzzzzzzlllleeee ==== $$$$sssseeeellllffff---->>>>{{{{''''ffffiiiizzzzzzzzlllleeee''''}}}};;;;

                       pppprrrriiiinnnntttt """"TTTThhhheeee wwwwoooorrrrdddd iiiissss """",,,, $$$$ffffiiiizzzzzzzzlllleeee---->>>>{{{{''''PPPPaaaasssssssswwwwoooorrrrdddd''''}}}},,,, """"\\\\nnnn"""";;;;
               }}}}

               ppppaaaacccckkkkaaaaggggeeee FFFFoooooooo;;;;
               @@@@IIIISSSSAAAA ==== qqqqwwww(((( BBBBaaaarrrr ))));;;;

               %%%%ffffiiiizzzzzzzzlllleeee ==== (((( ''''PPPPaaaasssssssswwwwoooorrrrdddd'''' ====>>>> ''''RRRRuuuummmmpppplllleeee'''' ))));;;;

               ssssuuuubbbb nnnneeeewwww {{{{
                       mmmmyyyy $$$$ttttyyyyppppeeee ==== sssshhhhiiiifffftttt;;;;
                       mmmmyyyy $$$$sssseeeellllffff ==== BBBBaaaarrrr---->>>>nnnneeeewwww;;;;
                       $$$$sssseeeellllffff---->>>>{{{{''''ffffiiiizzzzzzzzlllleeee''''}}}} ==== \\\\%%%%ffffiiiizzzzzzzzlllleeee;;;;
                       bbbblllleeeessssssss $$$$sssseeeellllffff,,,, $$$$ttttyyyyppppeeee;;;;
               }}}}

               ppppaaaacccckkkkaaaaggggeeee mmmmaaaaiiiinnnn;;;;

               $$$$aaaa ==== BBBBaaaarrrr---->>>>nnnneeeewwww;;;;
               $$$$bbbb ==== FFFFoooooooo---->>>>nnnneeeewwww;;;;
               $$$$aaaa---->>>>eeeennnntttteeeerrrr;;;;
               $$$$bbbb---->>>>eeeennnntttteeeerrrr;;;;


IIIINNNNHHHHEEEERRRRIIIITTTTIIIINNNNGGGG AAAA CCCCOOOONNNNSSSSTTTTRRRRUUUUCCCCTTTTOOOORRRR
       An inheritable constructor should use the second form of
       _b_l_e_s_s_(_) which allows blessing directly into a specified
       class.  Notice in this example that the object will be a
       BAR not a FOO, even though the constructor is in class
       FOO.

               ppppaaaacccckkkkaaaaggggeeee FFFFOOOOOOOO;;;;

               ssssuuuubbbb nnnneeeewwww {{{{
                       mmmmyyyy $$$$ttttyyyyppppeeee ==== sssshhhhiiiifffftttt;;;;
                       mmmmyyyy $$$$sssseeeellllffff ==== {{{{}}}};;;;
                       bbbblllleeeessssssss $$$$sssseeeellllffff,,,, $$$$ttttyyyyppppeeee;;;;
               }}}}




12/Feb/96                perl 5.002 with                        9





PERLBOT(1)     User Contributed Perl Documentation     PERLBOT(1)


               ssssuuuubbbb bbbbaaaazzzz {{{{
                       pppprrrriiiinnnntttt """"iiiinnnn FFFFOOOOOOOO::::::::bbbbaaaazzzz(((())))\\\\nnnn"""";;;;
               }}}}

               ppppaaaacccckkkkaaaaggggeeee BBBBAAAARRRR;;;;
               @@@@IIIISSSSAAAA ==== qqqqwwww((((FFFFOOOOOOOO))));;;;

               ssssuuuubbbb bbbbaaaazzzz {{{{
                       pppprrrriiiinnnntttt """"iiiinnnn BBBBAAAARRRR::::::::bbbbaaaazzzz(((())))\\\\nnnn"""";;;;
               }}}}

               ppppaaaacccckkkkaaaaggggeeee mmmmaaaaiiiinnnn;;;;

               $$$$aaaa ==== BBBBAAAARRRR---->>>>nnnneeeewwww;;;;
               $$$$aaaa---->>>>bbbbaaaazzzz;;;;


DDDDEEEELLLLEEEEGGGGAAAATTTTIIIIOOOONNNN
       Some classes, such as SDBM_File, cannot be effectively
       subclassed because they create foreign objects.  Such a
       class can be extended with some sort of aggregation
       technique such as the "using" relationship mentioned
       earlier or by delegation.

       The following example demonstrates delegation using an
       _A_U_T_O_L_O_A_D_(_) function to perform message-forwarding.  This
       will allow the Mydbm object to behave exactly like an
       SDBM_File object.  The Mydbm class could now extend the
       behavior by adding custom _F_E_T_C_H_(_) and _S_T_O_R_E_(_) methods, if
       this is desired.

               ppppaaaacccckkkkaaaaggggeeee MMMMyyyyddddbbbbmmmm;;;;

               rrrreeeeqqqquuuuiiiirrrreeee SSSSDDDDBBBBMMMM____FFFFiiiilllleeee;;;;
               rrrreeeeqqqquuuuiiiirrrreeee TTTTiiiieeee::::::::HHHHaaaasssshhhh;;;;
               @@@@IIIISSSSAAAA ==== qqqqwwww((((TTTTiiiieeee::::::::HHHHaaaasssshhhh))));;;;

               ssssuuuubbbb TTTTIIIIEEEEHHHHAAAASSSSHHHH {{{{
                       mmmmyyyy $$$$ttttyyyyppppeeee ==== sssshhhhiiiifffftttt;;;;
                       mmmmyyyy $$$$rrrreeeeffff ==== SSSSDDDDBBBBMMMM____FFFFiiiilllleeee---->>>>nnnneeeewwww((((@@@@____))));;;;
                       bbbblllleeeessssssss {{{{''''ddddeeeelllleeeeggggaaaatttteeee'''' ====>>>> $$$$rrrreeeeffff}}}};;;;
               }}}}

               ssssuuuubbbb AAAAUUUUTTTTOOOOLLLLOOOOAAAADDDD {{{{
                       mmmmyyyy $$$$sssseeeellllffff ==== sssshhhhiiiifffftttt;;;;

                       #### TTTThhhheeee PPPPeeeerrrrllll iiiinnnntttteeeerrrrpppprrrreeeetttteeeerrrr ppppllllaaaacccceeeessss tttthhhheeee nnnnaaaammmmeeee ooooffff tttthhhheeee
                       #### mmmmeeeessssssssaaaaggggeeee iiiinnnn aaaa vvvvaaaarrrriiiiaaaabbbblllleeee ccccaaaalllllllleeeedddd $$$$AAAAUUUUTTTTOOOOLLLLOOOOAAAADDDD....

                       #### DDDDEEEESSSSTTTTRRRROOOOYYYY mmmmeeeessssssssaaaaggggeeeessss sssshhhhoooouuuulllldddd nnnneeeevvvveeeerrrr bbbbeeee pppprrrrooooppppaaaaggggaaaatttteeeedddd....
                       rrrreeeettttuuuurrrrnnnn iiiiffff $$$$AAAAUUUUTTTTOOOOLLLLOOOOAAAADDDD ====~~~~ ////::::::::DDDDEEEESSSSTTTTRRRROOOOYYYY$$$$////;;;;

                       #### RRRReeeemmmmoooovvvveeee tttthhhheeee ppppaaaacccckkkkaaaaggggeeee nnnnaaaammmmeeee....
                       $$$$AAAAUUUUTTTTOOOOLLLLOOOOAAAADDDD ====~~~~ ssss////^^^^MMMMyyyyddddbbbbmmmm::::::::////////;;;;



12/Feb/96                perl 5.002 with                       10





PERLBOT(1)     User Contributed Perl Documentation     PERLBOT(1)


                       #### PPPPaaaassssssss tttthhhheeee mmmmeeeessssssssaaaaggggeeee ttttoooo tttthhhheeee ddddeeeelllleeeeggggaaaatttteeee....
                       $$$$sssseeeellllffff---->>>>{{{{''''ddddeeeelllleeeeggggaaaatttteeee''''}}}}---->>>>$$$$AAAAUUUUTTTTOOOOLLLLOOOOAAAADDDD((((@@@@____))));;;;
               }}}}

               ppppaaaacccckkkkaaaaggggeeee mmmmaaaaiiiinnnn;;;;
               uuuusssseeee FFFFccccnnnnttttllll qqqqwwww(((( OOOO____RRRRDDDDWWWWRRRR OOOO____CCCCRRRREEEEAAAATTTT ))));;;;

               ttttiiiieeee %%%%ffffoooooooo,,,, MMMMyyyyddddbbbbmmmm,,,, """"aaaaddddbbbbmmmm"""",,,, OOOO____RRRRDDDDWWWWRRRR||||OOOO____CCCCRRRREEEEAAAATTTT,,,, 0000666644440000;;;;
               $$$$ffffoooooooo{{{{''''bbbbaaaarrrr''''}}}} ==== 111122223333;;;;
               pppprrrriiiinnnntttt """"ffffoooooooo----bbbbaaaarrrr ==== $$$$ffffoooooooo{{{{''''bbbbaaaarrrr''''}}}}\\\\nnnn"""";;;;















































12/Feb/96                perl 5.002 with                       11