Perl Concatenate vs Append Operator

nande9 has asked for the wisdom of the Perl Monks concerning the following question:

Replies are listed 'Best First'.
Re: Perl Concatenate vs Append Operator by Your Mother (Archbishop) on Aug 19, 2014 at 17:21 UTC
FWIW, there are better ways to do what concatenation does… 90% of the time? Not that it’s wrong but that there are cleaner ways that are more flexible and easier to build on or manipulate or test or pass around; `print join " ", @strings;` for example v `$string .= $_ . " " for @stuff`. There are no good or bad operators but, for me, string concatenation, while it is naturally the way a lot of think/code at first, is code smell most of the time.	[reply] [d/l] [select]
Re: Perl Concatenate vs Append Operator by Jim (Curate) on Aug 19, 2014 at 16:59 UTC
Neither is more correct than the other. TMTOWTDI, that's all. I prefer to use the assignment operators because I think they're more intuitive and more idiomatic. And I prefer auto-increment and auto-decrement to the assignment operators. So I'd do this… `$total_days++;` [download] …instead of this… `$total_days += 1;` [download] …and I'd never do this… `$total_days = $total_days + 1;` [download] UPDATE: I concur with Your Mother's remarks about the concatenation operator. I hardly ever use it. In most cases, there's a better way to accomplish one's string-building tasks using other methods, particularly `join()`.	[reply] [d/l] [select]
Re: Perl Concatenate vs Append Operator by McA (Priest) on Aug 19, 2014 at 17:31 UTC
Hi, just as an addition. Compare the output of: `perl -MO=Terse -E'my $str = "McA"; $str = $str . " ";'` [download] and `perl -MO=Terse -E'my $str = "McA"; $str .= " ";'` [download] So the internal way of handling this (tried with Perl 5.10.1) is the same. Regards McA	[reply] [d/l] [select]
Re^2: Perl Concatenate vs Append Operator by Anonymous Monk on Aug 19, 2014 at 18:08 UTC
But! `perl -MO=Terse -E'our $str; $str = $str . " ";'` [download] and `perl -MO=Terse -E'our $str; $str .= " ";'` [download]	[reply] [d/l] [select]
Re^3: Perl Concatenate vs Append Operator by McA (Priest) on Aug 19, 2014 at 18:47 UTC
Hi, I'm so used to lexical variables that I didn't think about that. That's really interesting. Thank you for that insight. McA	[reply]
Re^2: Perl Concatenate vs Append Operator by Laurent_R (Canon) on Aug 19, 2014 at 21:32 UTC
I just tried it on Perl 5.14, I do not get exactly the same thing with your two one-liners: $ perl -MO=Terse -E'my $str = "McA"; $str = $str . " ";' LISTOP (0x600153910) leave [1] OP (0x60007fdb0) enter COP (0x60006e3c0) nextstate BINOP (0x6001f1ea0) sassign SVOP (0x60006e2e0) const [3] PV (0x6001f2c08) "McA" OP (0x60006f890) padsv [1] COP (0x6001f7fe0) nextstate BINOP (0x6001f7fa0) concat [1] OP (0x600153980) padsv [1] SVOP (0x6001f7f60) const [4] PV (0x6001f2b78) " " -e syntax OK $ perl -MO=Terse -E'my $str = "McA"; $str .= " ";' LISTOP (0x600153910) leave [1] OP (0x60007fdb0) enter COP (0x60006e3c0) nextstate BINOP (0x6001f1ea0) sassign SVOP (0x60006e2e0) const [3] PV (0x6001f2c08) "McA" OP (0x60006f890) padsv [1] COP (0x6001f7f60) nextstate BINOP (0x6001539c0) concat [2] OP (0x600153950) padsv [1] SVOP (0x600153980) const [4] PV (0x6001f2b78) " " -e syntax OK [download] There are some differences on the ante-penultimate and penultimate lines. But I am not really able to assess whether the difference is significant. The Deparse module also gives different output for these two lines in Perl 5.14.	[reply] [d/l]
Re: Perl Concatenate vs Append Operator by Anonymous Monk on Aug 19, 2014 at 18:55 UTC
I would be surprised if it did not translate to essentially the same set of internal interpreter-instructions.	[reply]
Re^2: Perl Concatenate vs Append Operator by Anonymous Monk on Aug 19, 2014 at 21:08 UTC
A little late to the party? McA and another anon already showed the appropriate commands more than 45 minutes before your post.	[reply]
Re^3: Perl Concatenate vs Append Operator by sundialsvc4 (Abbot) on Aug 19, 2014 at 21:15 UTC
In other words ... "yes." As any sensible compiler design team would have known to do, and did.
Re: Perl Concatenate vs Append Operator by Anonymous Monk on Aug 19, 2014 at 17:10 UTC
As far as I kn(o\|e)w, Perl ha(s\|d) only concatenate operator. There (i\|wa)s no append operator.	[reply]


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