strange behavior in perl json encoding [duplicate] - json

Question

This question already has answers here:
Why does the JSON module quote some numbers but not others?
(2 answers)
Closed 8 years ago.
It seems that printing a hash value to a file may change something internally.
The following code snippet will print (notice there is double quote around 1.6):
{"john":4,"mary":"1.6"}
Code snippet:
use JSON::XS;
$a = {};
$a->{john} += "4";
$a->{mary} += "1.6";
open ($fd, ">tmp.txt") || die "Failed to open file to write $!\n";
print $fd "$a->{mary}";
close $fd;
$b = encode_json($a);
print "$b\n";
If I comment out the 3 lines on writing to a file in the above:
open ($fd, ">tmp.txt") || die "Failed to open file to write $!\n";
print $fd "$a->{mary}";
close $fd;
it will print without double-quote around 1.6.
{"john":4,"mary":1.6}
My perl is 5.14.2 running on Ubuntu 12.04 64bit, the JSON::XS module has version 3.01.
Wonder if what is causing this. Thanks.

Answer 1

It seems that printing a hash value to a file may change something internally.
No, but passing a string to the addition operator does.
$ perl -MDevel::Peek -e'$x="1.2"; Dump($x); 0+$x; Dump($x);' 2>&1 | grep FLAGS
FLAGS = (POK,pPOK)
FLAGS = (NOK,POK,pIOK,pNOK,pPOK)
POK = Contains a string.
NOK = Contains a floating point number.
Passing a copy of the string will avoid this.
$ perl -MDevel::Peek -e'$x="1.2"; Dump($x); 0+"$x"; Dump($x);' 2>&1 | grep FLAGS
FLAGS = (POK,pPOK)
FLAGS = (POK,pPOK)

Answer 2

Thanks to the links by #ThisSuitIsBlackNot and #Paul Roub, I made a slight change so that the encoded json string doesn't have the double quote around numbers:
open ($fd, ">tmp.txt") || die "Failed to open file to write $!\n";
$x = $a->{mary};
print $fd $x;
close $fd;
Basically I just assigned a hash value to an intermediate variable and print the intermediate variable.