AnomalousMonk has asked for the wisdom of the Perl Monks concerning the following question:
This question pertains to the hard copy of the first English edition, printed July 2005, chapter 9, pages 182 - 183, the "Named Arguments" section. I have checked the on-line errata lists and there are no corrections or alterations for these pages.
The discussion of "named arguments" contrasts building an anonymous hash of name/parameter pairs in the argument list of a function call with directly assigning the argument list (i.e., @_) to a hash within the body of the function.
With respect to building an anonymous hash of named arguments, page 183, second paragraph, states that errors "... will be reported (usually at compile time) in the caller's context ..." (emphasis added), but I don't see that this is so. (However, everything else works as advertised: the anonymous hash version of named arguments produces a warning at the point of the function invocation.)
Certainly, a malformed function call like
func({ one => 'uno', two => 'dos', three => });
from the example code below does compile and only warns at run time.
Can anyone give an example of a compile time error (or
warning) associated with this invocation technique, or any
explanation or example of what TheDamian was referring to?
Various malformed examples, code and output:
Output:use warnings; use strict; print "program running \n"; # these compile and run WITHOUT any warnings na_anon ({ one => 'uno', two => 'dos', => }); na_anon ({ one => 'uno', two => 'dos', , }); na_anon ({ one => 'uno', => two => 'dos' }); na_anon ({ one => 'uno', , two => 'dos' }); na_anon ({ one => 'uno', => => two => 'dos' }); na_anon ({ one => 'uno', , , two => 'dos' }); na_assign( one => 'ein', two => 'zwei', => ); na_assign( one => 'ein', two => 'zwei', , ); na_assign( one => 'ein', => two => 'zwei' ); na_assign( one => 'ein', , two => 'zwei' ); na_assign( one => 'ein', => => two => 'zwei' ); na_assign( one => 'ein', , , two => 'zwei' ); # these compile and run WITH run-time warnings na_anon ({ one => 'uno', two => 'dos', three => }); na_anon ({ one => 'uno', two => 'dos', three => 20..21 }); na_assign( one => 'ein', two => 'zwei', three => ); na_assign( one => 'ein', two => 'zwei', three => 20..21 ); print "program done \n"; sub na_anon { my %args = %{ $_[0] }; my $n = 'one'; print "anon hash: $n translates to $args{$n} \n"; } sub na_assign { my %args = @_; my $n = 'two'; print "hash assign: $n translates to $args{$n} \n"; }
>perl np_ah_vs_ha_1.pl program running anon hash: one translates to uno anon hash: one translates to uno anon hash: one translates to uno anon hash: one translates to uno anon hash: one translates to uno anon hash: one translates to uno hash assign: two translates to zwei hash assign: two translates to zwei hash assign: two translates to zwei hash assign: two translates to zwei hash assign: two translates to zwei hash assign: two translates to zwei Odd number of elements in anonymous hash at np_ah_vs_ha_1.pl line 71. anon hash: one translates to uno Odd number of elements in anonymous hash at np_ah_vs_ha_1.pl line 72. anon hash: one translates to uno Odd number of elements in hash assignment at np_ah_vs_ha_1.pl line 85. hash assign: two translates to zwei Odd number of elements in hash assignment at np_ah_vs_ha_1.pl line 85. hash assign: two translates to zwei program done
Update: Slight clarification in wording of code comments.
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