Re^2: Optimizing Perl Code - single versus double quotes really that important?

Speed-wise, I don't think it makes much difference

Speedwise, it makes no difference. They produce exactly the same code.

$ perl -MO=Concise,-exec -e'$x = qq{a $b c}'
1  <0> enter
2  <;> nextstate(main 1 -e:1) v
3  <$> const[PV "a "] s
4  <#> gvsv[*b] s
5  <2> concat[t3] sK/2
6  <$> const[PV " c"] s
7  <2> concat[t4] sKS/2
8  <#> gvsv[*x] s
9  <2> sassign vKS/2
a  <@> leave[1 ref] vKP/REFC
-e syntax OK

$ perl -MO=Concise,-exec -e'$x = q{a }.$b.q{ c}'
1  <0> enter
2  <;> nextstate(main 1 -e:1) v
3  <$> const[PV "a "] s
4  <#> gvsv[*b] s
5  <2> concat[t3] sK/2
6  <$> const[PV " c"] s
7  <2> concat[t4] sKS/2
8  <#> gvsv[*x] s
9  <2> sassign vKS/2
a  <@> leave[1 ref] vKP/REFC
-e syntax OK
[download]

Comment on Re^2: Optimizing Perl Code - single versus double quotes really that important? Download Code

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Re^3: Optimizing Perl Code - single versus double quotes really that important? by DStaal (Chaplain) on Feb 05, 2009 at 18:21 UTC
Well... `perl -MO=Concise,-exec -e '$x=qq{a $b c}' 1 <0> enter 2 <;> nextstate(main 1 -e:1) v:{ 3 <$> const[PV "a "] s 4 <#> gvsv[b] s 5 <2> concat[t3] sK/2 6 <$> const[PV " c"] s 7 <2> concat[t4] sKS/2 8 <#> gvsv[x] s 9 <2> sassign vKS/2 a <@> leave[1 ref] vKP/REFC -e syntax OK perl -MO=Concise,-exec -e '$x=q{a $b c}' 1 <0> enter 2 <;> nextstate(main 1 -e:1) v:{ 3 <$> const[PV "a $b c"] s 4 <#> gvsv[*x] s 5 <2> sassign vKS/2 6 <@> leave[1 ref] vKP/REFC -e syntax OK` [download] So obviously there is some minor difference at compile-time. (Which would be the only difference I expect.) Once compiled equivalent expressions produce equivalent op-code, it's just that the compile process isn't exactly the same. Unlikely to be noticeable though, and really irrelevant to my original reply.	[reply] [d/l]
Re^4: Optimizing Perl Code - single versus double quotes really that important? by ikegami (Patriarch) on Feb 05, 2009 at 18:30 UTC
Apples and oranges. Those snippets don't build the same string. Of course they result in different code.	[reply]
Re^5: Optimizing Perl Code - single versus double quotes really that important? by DStaal (Chaplain) on Feb 05, 2009 at 18:45 UTC
Which was my point: The compiler looks at it differently. So there is a difference at compile time, as the compiler decides whether or not it needs to interpolate. I don't know how much time that takes. (If any: It is possible that both code-paths are equivalent in time, after all.) In theory that could be a major hit at startup. I doubt it however. And it depends on the situation: In the current context we are talking about a script that is being used in some CGI environment, so if the hit was really bad it is likely the script could be run under mod_perl, which would remove it from consideration. (If it isn't already.)	[reply]