override(3) User Contributed Perl Documentation override(3) NNNNAAAAMMMMEEEE ex::override - Perl pragma to override core functions SSSSYYYYNNNNOOOOPPPPSSSSIIIISSSS use ex::override ucfirst => sub { # make sure only the first # letter is uppercased ucfirst( lc( shift ) ); }; ucfirst( 'MAKE THIS RIGHT' ); # Make this right no ex::override 'ucfirst'; ucfirst( 'MAKE THIS RIGHT' ); # MAKE THIS RIGHT DDDDEEEESSSSCCCCRRRRIIIIPPPPTTTTIIIIOOOONNNN "ex::override" is an easy way to override core perl func- tions. OOOOvvvveeeerrrrrrrriiiiddddiiiinnnngggg aaaa ffffuuuunnnnccccttttiiiioooonnnn use ex::override length => \&mylength, open => \&myopen; Overriding a core function happens at compile time. Argu- ments are passed to "ex::override" in a name based, or hash style. The key is the name of the core function to override, the value is your subroutine to replace the core's. UUUUssssiiiinnnngggg aaaannnn oooovvvveeeerrrrrrrriiiiddddeeeennnn ffffuuuunnnnttttiiiioooonnnn Nothing changes on the surface. If you override "stat", then you still use "stat" the same way. NNNNOOOOTTTTEEEE:::: This is only true if you are keeping the same proto- type as the function you've overriden. To do this, you must define your prototype: use ex::override values => sub (\%) { values %{+shift} }; If you don't use this same prototype or force yourself to use the function the same, you can extend the functional- ity of a core function: # length of all arguments passed to length() use ex::override length => sub { length join '', @_ }; OOOOvvvveeeerrrrrrrriiiiddddiiiinnnngggg aaaa ffffuuuunnnnccccttttiiiioooonnnn gggglllloooobbbbaaaallllyyyy DDDDoooonnnn''''tttt ddddoooo tttthhhhiiiissss wwwwiiiitttthhhhoooouuuutttt aaaa vvvveeeerrrryyyy ggggoooooooodddd rrrreeeeaaaassssoooonnnn!!!! "ex::override" allows you the ability to override core functions globaly. Any packages that inherit from yours will use your function override. There are good reasons for doing this, if you think you need to, make sure you have a good reason. use ex::override GLOBAL_length => sub { # prevent someone from passing a list croak "Don't do that!" if @_ > 1; length shift }; NNNNOOOOTTTTEEEE:::: If you globaly override a function in a package, only that package can remove it. RRRReeeemmmmoooovvvviiiinnnngggg yyyyoooouuuurrrr oooovvvveeeerrrrrrrriiiiddddeeee This works the same way that "no strict" works. no ex::override; # remove _all_ overrides no ex::override 'values'; no ex::override 'GLOABL_length'; TTTTIIIIPPPPSSSS Get a list of overrideable function If you have the Perl source laying around, go to it's root dir and try this: perl -lne 'print /_(\w+)/ if /return -K/' toke.c You'll have to weed out which ones are functions ( vs. operators, etc. ). Get a functions prototype perl -lwe 'print prototype "CORE::length"' This prints the prototype, or "Use of uninitialized variable..." if there isn't one. TTTTOOOODDDDOOOO Find a way to preserve prototypes so the user doesn't have to know them. AAAAUUUUTTTTHHHHOOOORRRR Casey West, <_c_a_s_e_y_@_g_e_e_k_n_e_s_t_._c_o_m> CCCCOOOOPPPPYYYYRRRRIIIIGGGGHHHHTTTT Copyright (c) 2000 Casey West . All rights reserved. This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself. 2003-03-14 perl v5.6.1 override(3)