article

examples/implicit_return.pl

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+use strict;
+use warnings;
+use feature 'say';
+
+
+sub function {
+    my ($x, $y) = @_;
+
+    if ($x < $y) {
+        my $total = $x + $y;
+    }
+}
+
+{
+    my $res = function(2, 3);
+    say defined $res ? "defined" : "undef";
+    say $res eq "" ? "empty string" : "NOT the empty string";
+    say $res;
+    say "-------------------";
+}
+{
+    my $res = function(3, 2);
+    say defined $res;
+    say $res eq "" ? "empty string" : "NOT the empty string";
+    say $res;
+    say "-------------------";
+}

sites/en/pages/curious-case-of-implicit-return.txt

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+=title The curious case of implicit return
+=timestamp 2023-12-03T07:30:01
+=indexes sub, return
+=status show
+=author szabgab
+=archive 1
+=description If a function in Perl does not explicitly call return then it will implicitly return the result of the last statement evaluated.
+=comments_disqus_enable 0
+=show_related 1
+
+=abstract start
+
+My son works at a company where they analyze source code and report on potential <a href="https://privya.ai/">data privacy violations</a>.
+For this they need to parse source code in various programming languages. He mentioned that one day they might need to support Perl too.
+I thought about the difficulties in parsing Perl and one case came to my mind was the strange implicit return from a function that Perl has.
+
+Then I also thought that <a href="https://www.rust-lang.org/">Rust</a> also has some strange ideas. BTW Do you know that I have a new web site called
+<a href="https://rust.code-maven.com/">Rust Maven</a> where I write about Rust? Now you know.
+
+Anyway, back to Perl:
+
+=abstract end
+
+What do you think this function will return and what will this code print?
+
+<include file="examples/implicit_return.pl">
+
+I know it is a very contrived example, but in the few minutes I spent on it I could not come up with a more realistic one. Send me a better example!
+
+
+<h2>Spoiler Alert</h2>
+
+If a function in Perl does not explicitly call <b>return</b> then it will implicitly return the result of the last statement evaluated.
+
+In the above code, if the <b>if</b> condition inside the "function" evaluates to <b>true</b> then the code inside the block will be executed
+and thus the assignment to <b>$total</b> will be the last executed statement and so the value of <b>$total</b> will be returned.
+
+On the other hand if the <b>if</b> condition inside the "function" evaluates to <b>false</b> then this will be the last statement
+in the function and thus this <b>false</b> value will be returned that will happen to be the <b>empty string</b>.
+
+In the example I added a check to show whether the returned values is <a href="/defined">defined</a> or if it is <a href="/undef">undef</a>.
+A separate check is included to show if it <b>equals</b> to the empty string or not using the <a href="/the-ternary-operator-in-perl">ternary operator</a>.
+
+
+<code>
+defined
+NOT the empty string
+5
+-------------------
+1
+empty string
+
+-------------------
+</code>
+
+