Re: order of evaluation of operands

I can answer this with much zeal and vigor. (Or I just wanted to use those two words.)

Use the B::Terse module, I made the following check:

jeffp@friday [10:44am] parsers #264> perl -MO=Terse
sub a { print 1 }
sub b { print 2 }
$c = a() + b();
- syntax OK
LISTOP (0x13b940) pp_leave
    OP (0x130ef8) pp_enter
    COP (0x13b970) pp_nextstate
    BINOP (0x142ce0) pp_sassign
        BINOP (0x142d00) pp_add [3]
            UNOP (0x142c20) pp_entersub [1]
                UNOP (0x13b9d0) pp_null [141]
                    OP (0x130f58) pp_pushmark
                    UNOP (0x142c40) pp_null [17]
                        GVOP (0x142c60) pp_gv  GV (0x12dbac) *a
            UNOP (0x142d20) pp_entersub [2]
                UNOP (0x13ba90) pp_null [141]
                    OP (0x130f70) pp_pushmark
                    UNOP (0x142d40) pp_null [17]
                        GVOP (0x142d60) pp_gv  GV (0x14bbc4) *b
        UNOP (0x12ea00) pp_null [15]
            GVOP (0xbed00) pp_gvsv  GV (0xc6304) *c
[download]

Yes, Perl will call a() before it calls b(). That's why you can safely say: ($a,$b) = (shift, shift) to get the first two values from @_, IN THE RIGHT ORDER. (But you'd use splice(), really.)

Comment on Re: order of evaluation of operands Download Code

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RE: Re: order of evaluation of operands by jlistf (Monk) on Jul 21, 2000 at 21:00 UTC
That's why you can safely say: ($a,$b) = (shift, shift) to get the first two values from @_, IN THE RIGHT ORDER. the comma operator is one that definitely evaluates left to right. it does this even in C/C++ (in addition to `&&`, `and`, `\|\|`, `or` and `?:`). i know that those evaluate left to right. but are all operators guaranteed to evaluate left to right. just because your computer does it that way does not necesarily mean that all will. granted Perl has less computer/software dependant items like C and C++, but i'd like to know for sure what the case is. preferably some mention in documentation or an answer from someone who's read the source code or a link to a tutorial or something.	[reply] [d/l] [select]
RE: RE: Re: order of evaluation of operands by japhy (Canon) on Jul 21, 2000 at 21:57 UTC
Check the perlop documentation.	[reply]