The placement of a sub is important onlymainly when you call it without parentheses, i.e. as a bareword. When such a call is being parsed, the subs already parsed are recognised and the bareword is parsed as their call, otherwise without strict, the bareword is stringified, and with strict, you get an error. 
#!/usr/bin/perl
use warnings;

print "", frob();  # 12
print "", frob;    # frob

use strict;

print "", frob();  # 12
# print "", frob;

sub frob {
    12
}

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Uncommenting the last last print line would make the source unparsable with 
Bareword "frob" not allwoed while "strict subs" in use

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Updated: as shown in the text, thanks kcott.

map{substr$_->[0],$_->[1]||0,1}[\*||{},3],[[]],[ref qr-1,-,-1],[{}],[sub{}^*ARGV,3]

In reply to Re^2: why avoid & on function call by choroba
in thread why avoid & on function call by fireblood

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