They call me obsessed. They call me crazy. But fear not, the Over-Optimizer is here. I, like many programmers, will optimise the smallest code just to eek out the smallest gains. In doing this you learn the art of optimsation.Also, i am a programmer, not an english teacher, so please ignore any spelling errors. See below :

Checking : $$var vs. ${$var}

Test Code : 
#!/usr/bin/perl

$a = "foo";
$b = \$a;


print "b : $$b\n";

print "b2 : ${$b}\n";

[download]

Tests : perl -MO=Deparse,-p test_ref.pl
    if inconclusive ...
perl -Dt  test_ref.pl

Test 1 : 
perl -MO=Deparse,-p test_ref.pl

($a = 'foo');
($b = (\$a));
print("b : $$b\n");
print("b2 : ${$b;}\n");
test_ref.pl syntax OK

[download]

hmmmm, no real help there. Actually, based on the ";" added on the second print, ${$var} might be slower (which would make my guess wrong).

Test 2 : 
perl -Dt  test_ref.pl

(test_ref.pl:0) enter
(test_ref.pl:0) nextstate
(test_ref.pl:3) const(PV("foo"\0))
(test_ref.pl:3) gvsv(main::a)
(test_ref.pl:3) sassign
(test_ref.pl:3) nextstate
(test_ref.pl:4) gvsv(main::a)
(test_ref.pl:4) srefgen
(test_ref.pl:4) gvsv(main::b)
(test_ref.pl:4) sassign
(test_ref.pl:4) nextstate
(test_ref.pl:7) pushmark
(test_ref.pl:7) const(PV("b : "\0))
(test_ref.pl:7) gvsv(main::b)
(test_ref.pl:7) rv2sv
(test_ref.pl:7) concat
(test_ref.pl:7) const(PV("\n"\0))
(test_ref.pl:7) concat
(test_ref.pl:7) print
b : foo
(test_ref.pl:7) nextstate
(test_ref.pl:9) pushmark
(test_ref.pl:9) const(PV("b2 : "\0))
(test_ref.pl:9) gvsv(main::b)
(test_ref.pl:9) rv2sv
(test_ref.pl:9) concat
(test_ref.pl:9) const(PV("\n"\0))
(test_ref.pl:9) concat
(test_ref.pl:9) print
b2 : foo
(test_ref.pl:9) leave

[download]

Eurica !

Now, for those who did not spot it, here is what i am seeing :
    The first line which has (test_ref.pl:7) is entering the print statement. Reading from there to the end, there are two duplicated sections, meaning the exact same path is used for both de-referencers. So, to show it more clearly (sorry about any code wrapping) : 
(test_ref.pl:4) nextstate             (test_ref.pl:7) nextstate
(test_ref.pl:7) pushmark              (test_ref.pl:9) pushmark
(test_ref.pl:7) const(PV("b : "\0))   (test_ref.pl:9) const(PV("b2 : "
+\0))
(test_ref.pl:7) gvsv(main::b)         (test_ref.pl:9) gvsv(main::b)
(test_ref.pl:7) rv2sv                 (test_ref.pl:9) rv2sv
(test_ref.pl:7) concat                (test_ref.pl:9) concat
(test_ref.pl:7) const(PV("\n"\0))     (test_ref.pl:9) const(PV("\n"\0)
+)
(test_ref.pl:7) concat                (test_ref.pl:9) concat
(test_ref.pl:7) print                 (test_ref.pl:9) print
b : foo                               b2 : foo

[download]

So, $$var and ${$var} are the same after optimisation.
always more than one way to skin an amoebae
-- MZSanford

In reply to Re: Efficiency of $$var, ${$var} by MZSanford
in thread Efficiency of $$var, ${$var} by bladx

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