Addition documentation explaining aritmetic negation on strings. Also,

additional test cases based partially on code by Piotr Fusik in
RT #36675: -'-10' eq '+10'.

p4raw-id: //depot/perl@26387

diff --git a/pod/perlop.pod b/pod/perlop.pod
index d0b4c64..6afe473 100644 (file)
--- a/pod/perlop.pod
+++ b/pod/perlop.pod
@@ -199,7 +199,11 @@ the operand is an identifier, a string consisting of a minus sign
 concatenated with the identifier is returned.  Otherwise, if the string
 starts with a plus or minus, a string starting with the opposite sign
 is returned.  One effect of these rules is that -bareword is equivalent
-to the string "-bareword".
+to the string "-bareword".  If, however, the string begins with a
+non-alphabetic characters, Perl will attempt to convert the string to a numeric
+and the arithmetic negation is performed.  If the string cannot be cleanly 
+converted to a numeric, Perl will give the warning B<Argument "the string"
+isn't numeric in negation (-) at ...>.  
 X<-> X<negation, arithmetic>
 
 Unary "~" performs bitwise negation, i.e., 1's complement.  For

diff --git a/t/op/negate.t b/t/op/negate.t
new file mode 100644 (file)
index 0000000..fb8d4b4
--- /dev/null
+++ b/t/op/negate.t
@@ -0,0 +1,31 @@
+#!./perl -w
+
+BEGIN {
+    chdir 't' if -d 't';
+    @INC = '../lib';
+    require './test.pl';
+}
+
+plan tests => 16;
+
+# Some of these will cause warnings if left on.  Here we're checking the
+# functionality, not the warnings.
+no warnings "numeric";
+
+# test cases based on [perl #36675] -'-10' eq '+10'
+is(- 10, -10, "Simple numeric negation to negative");
+is(- -10, 10, "Simple numeric negation to positive");
+is(-"10", -10, "Negation of a positive string to negative");
+is(-"10.0", -10, "Negation of a positive decimal sting to negative");
+is(-"10foo", -10, "Negation of a numeric-lead string returns negation of numeric");
+is(-"-10", "+10", 'Negation of string starting with "-" returns a string starting with "+" - numeric');
+is(-"-10.0", "+10.0", 'Negation of string starting with "-" returns a string starting with "+" - decimal');
+is(-"-10foo", "+10foo", 'Negation of string starting with "-" returns a string starting with "+" - non-numeric');
+is(-"xyz", "-xyz", 'Negation of a negative string adds "-" to the front');
+is(-"-xyz", "+xyz", "Negation of a negative string to positive");
+is(-"+xyz", "-xyz", "Negation of a positive string to negative");
+is(-bareword, "-bareword", "Negation of bareword treated like a string");
+is(- -bareword, "+bareword", "Negation of -bareword returns string +bareword");
+is(-" -10", 10, "Negation of a whitespace-lead numeric string");
+is(-" -10.0", 10, "Negation of a whitespace-lead decimal string");
+is(-" -10foo", 10, "Negation of a whitespace-lead sting starting with a numeric")