Re^9: Reference of constants and literals

(Upd: I didn't take into account that \1 is a constant itself. Please ignore this post )

anyway I think it's a notable result of this discussion that the location of constants and literals will not be fixed at compiletime!

That's not true. Constants are allocated once at compile time.

for (1..3) {
   print(\1, "\n");

   push @x, 'x';  # Prevent reuse of memory addresses.
}
[download]

SCALAR(0x236d94)
SCALAR(0x236d94)
SCALAR(0x236d94)
[download]

They are tied to the opcode, and the same constant is returned every time.

PP(pp_const)
{
    dVAR;
    dSP;
    XPUSHs(cSVOP_sv);
    RETURN;
}
[download]

If you see otherwise, it's because you're looking at a *copy* of the constant.

Note that different instances of the same literal results in different constants.

for (1..3) {
   print(\1, ' ', \1, "\n");

   push @x, 'x';  # Prevent reuse of memory addresses.
}
[download]

SCALAR(0x236d94) SCALAR(0x183179c)
SCALAR(0x236d94) SCALAR(0x183179c)
SCALAR(0x236d94) SCALAR(0x183179c)
[download]

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Re^10: Reference of constants and literals by LanX (Saint) on Nov 24, 2008 at 17:51 UTC
I have to admit, I don't understand your code, I know `\1` in the context of RegEx but otherwise couldn't find any reference for it in the docs. do you have a link, please? please explain > If you see otherwise, it's because you're looking at a copy* of the constant.* $_[0] is supossed to be an alias to the parameter `DB<1> sub pr { print \$_[0] } DB<2> $a="x" DB<3> print \$a SCALAR(0x852b11c) DB<4> pr $a SCALAR(0x852b11c)` [download] Or do you mean that aliased symbols of variables in perl don't neccessarily have the same reference? I suppose this can possibly be done with typeglogs ... do mean this or a similar mechanism? Cheers Rolf	[reply] [d/l] [select]
Re^11: Reference of constants and literals by ikegami (Patriarch) on Nov 24, 2008 at 18:06 UTC
I have to admit, I don't understand your code, I know \1 in the context of RegEx but otherwise couldn't find any reference for it in the docs. do you have a link, please? `1` is a constant. `\` takes a reference. Or do you mean that aliased symbols of variables in perl don't neccessarily have the same reference? I didn't speculate or investigate what a copy would be made. However, I made a mistake. I forgot to take into account that `\1` is a constant itself. `>perl -MO=Concise -e"$x = \1" 6 <@> leave[1 ref] vKP/REFC ->(end) 1 <0> enter ->2 2 <;> nextstate(main 1 -e:1) v ->3 5 <2> sassign vKS/2 ->6 3 <$> const[RV \1] s ->4 <----- - <1> ex-rv2sv sKRM/1 ->5 4 <#> gvsv[x] s ->5 -e syntax OK` [download] My conclusion was based on observed results, which were based on a faulty assumption. Please ignore. On the plus side, it's a simple of way of generating a unique id for a spot in a file! Isn't that what you were after? It's not clear how you'd find out which spot is associated with which id, though.	[reply] [d/l] [select]
Re^12: Reference of constants and literals by LanX (Saint) on Nov 24, 2008 at 21:21 UTC
`I have to admit, I don't understand your code, I know \1 in the co +ntext of RegEx but otherwise couldn't find any reference for it in th +e docs. do you have a link, please? 1 is a constant. \ takes a reference.` [download] argh ... (banging the head against the keyboard) ... well sometimes I don't see the wood for the trees 8 )	[reply] [d/l]