Why does this not work?
my $myHashEncoded = encode_json \%myHash;
my %myHashDecoded = decode_json($myHashEncoded);
I get the error:
Reference found where even-sized list expected at ...
So I changed it to:
my $myHashEncoded = encode_json \%myHash;
my $myHashDecoded = decode_json($enableInputEncoded);
But then obviously %myHash is not the same as $myHashDecoded.
How do I restore a proper hash from the JSON string?
Assuming you are using JSON.pm, the documentation says:
The opposite of encode_json: expects an UTF-8 (binary) string and tries to parse that as an UTF-8 encoded JSON text, returning the resulting reference.
So you are getting back what you put in. You're putting in a hashref and you're getting a hashref back.
If you want a regular hash, then you just dereference it as you would any other hashref:
my $myHashRefDecoded = decode_json($myHashEncoded);
my %myHashDecoded = %$myHashRefDecoded;
You are encoding a reference to a hash (encode_json \%myHash), which is correct. So when you decode your JSON string you are receiving a reference to a hash. Prepend a % sigil to a hash reference to dereference it.
$myHashReferenceDecoded = decode_json($myHashReferenceEncoded);
%myHashDecoded = %$myHashReferenceDecoded;
On the following line, you do two things: you create a reference to the hash (\), and you encode the result (encode_json):
my $myHashEncoded = encode_json(\%myHash);
One the following line, you decode the JSON (decode_json), but you don't "undo" the reference.
my %myHashDecoded = decode_json($myHashEncoded);
The real inverse operation would involve a hash derereference.
my %myHashDecoded = %{ decode_json($myHashEncoded) };
But that needlessly makes a (shallow) copy of the hash. Maybe you should just work with the reference instead.
my $myHashDecoded = decode_json($myHashEncoded);
By the way, the reason a reference is used is that it's impossible to pass a hash to a sub or to return a hash from a sub. Only list of scalar can be passed and returned.
The JSON API is consistent. If you use a reference to a hash when encoding, you also get a hash reference when decoding.
So if you want to store the result in a pure hash variable, you have to dereference the result of decode_json with %{ ... }.
Solution:
my $myHashEncoded = encode_json \%myHash;
my %myHashDecoded = %{ decode_json($myHashEncoded) };
Note that dereferencing a hash is a costly operation. You should really consider if using directly the reference is not enough in your code.
encode_jsonanddecode_jsonfrom?my %myHashDecoded = %{ decode_json($enableInputEncoded) };