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    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";

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

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

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

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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