Unusual Behavior in Interpolative Context

sierrathedog04 has asked for the wisdom of the Perl Monks concerning the following question:

Chapter 2 of the Camel Book uses the term 'interpolative context' to describe what goes in inside of double quotes.

If an object member function returns a string in scalar context then should it behave similarly in interpolative context?

It would seem logical to me that it should, yet my experience is that it does not, e.g.:

my $parser = new XML::DOM::Parser;
my $doc = $parser->parse("<hello></hello>");
my $root = $doc->getFirstChild;
my $rootName = $root->getNodeName; 
print  $root->getNodeName . "\n"; # prints 'hello' in scalar context
print "$root->getNodeName\n"; # prints gibberish in interpolative cont
+ext
[download]

Why the difference? Is this a design flaw in Perl, or am I misunderstanding what is going on?

Shouldn't the scalar return value of the getNodeName member function appear in both scalar and interpolative context?

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Re: Unusual Behavior in Interpolative Context by btrott (Parson) on Feb 01, 2001 at 01:32 UTC
Method calls aren't interpolated within double quotes. So getNodeName isn't even getting called in the second context. You can force interpolation: `print "@{ [ $root->getNodeName ] }\n";` [download] I used to do this but then I started to think it rather ugly and started using printf and sprintf instead: `printf "%s\n", $root->getNodeName;` [download] because I think it's prettier.	[reply] [d/l] [select]
Re: Re: Unusual Behavior in Interpolative Context by sierrathedog04 (Hermit) on Feb 01, 2001 at 20:00 UTC
Thanks for explaining to me that method calls are not resolved in interpolative context. I came across an interesting tidbit in Chapter 8 of the Camel book that is related to your workaround: It said Avoid printf if print will work. Quite apart from the extra overhead of printf, some implementations have field length limitations that print gets around. So based on what Larry Wall says even if your way of forcing interpolation is ugly it is still preferable.	[reply]
Re: Re: Re: Unusual Behavior in Interpolative Context by chromatic (Archbishop) on Feb 04, 2001 at 11:01 UTC
Also remember that print takes a list of arguments. I don't find it too much of a hassle to say something like: `print "Result: ", $obj->foo(), "\n";` It's a little more efficient, too, but if that's the last thing you need to optimize you're way ahead of the game.	[reply] [d/l]