Overriding built-ins

chas has asked for the wisdom of the Perl Monks concerning the following question:

Replies are listed 'Best First'.
Re: Overriding built-ins by tlm (Prior) on Jun 01, 2005 at 18:29 UTC
You may find this node useful. The short answer is that `print` is one of a handful of builtins that cannot be overridden. See in particular diotalevi's comments in the thread referred to above. the lowliest monk	[reply]
Re^2: Overriding built-ins by chas (Priest) on Jun 01, 2005 at 18:40 UTC
Thanks tlm (and everyone else)! I should have searched perlmonks before asking (I did look in the docs but didn't find the answer.) The print function is an obvious choice to try out overriding since it would be easy to see the effect; presumably one wouldn't actually want to do this (for other than experimentation), though. chas	[reply]
Re: Overriding built-ins by Roy Johnson (Monsignor) on Jun 01, 2005 at 18:32 UTC
You can't override print. Caution: Contents may have been coded under pressure.	[reply]
Re: Overriding built-ins by ikegami (Patriarch) on Jun 01, 2005 at 18:32 UTC
Not all core functions can be overridden. `print` is one of those that cannot. Even the following doesn't work `package MyPrint; sub print { shift; CORE::print("[\n"); CORE::print(@_); CORE::print("]\n"); } package main; bless *STDOUT{IO}, 'MyPrint'; print("Hello World!\n"); # builtin print STDOUT ("Hello World!\n"); # builtin` [download] but this does `STDOUT->print("Hello World!\n"); # custom` [download] I think `tie`ing also works.	[reply] [d/l] [select]
Re: Overriding built-ins by dragonchild (Archbishop) on Jun 01, 2005 at 18:30 UTC
print is one of those non-overridable built-ins. There's about a half-dozen or so that can't be overriden. shrugs In general, if you think something isn't in Perl, try it out, because it usually is. :-) "What is the sound of Perl? Is it not the sound of a wall that people have stopped banging their heads against?"	[reply]
Re: Overriding built-ins by Joost (Canon) on Jun 01, 2005 at 18:32 UTC
I don't know if you can override print: perlsub says: ... some built-ins (e.g. "exists" or "grep") can’t be overridden. "What should it profit a man, if he should win a flame war, yet lose his cool?"	[reply]
Re: Overriding built-ins by ysth (Canon) on Jun 01, 2005 at 18:39 UTC
Usually you want to use the same prototype for an overriding function as the builtin has. If prototype("CORE::foo") is not defined, foo is usually not overridable (though require is an exception).	[reply]
Re: Overriding built-ins by diotalevi (Canon) on Jun 02, 2005 at 04:50 UTC
Other people linked to my old node at Re: !Overriding Builtin print. Initial Devel::UncheckedOps, a macro for perl presents a way that print() and other unoverridables can be be overriden anyway.	[reply]


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