Fixes issue Use structure in TO_JSON method when available #38 at: ht…

lib/JSON/Tiny.pm

@@ -52,6 +52,10 @@ multi to-json(Mu:D $s) {
     die "Can't serialize an object of type " ~ $s.WHAT.perl
 }
 
+multi to-json ( $_ where *.can('TO_JSON') ) {
+    to-json .TO_JSON
+}
+
 sub from-json($text) is export {
     my $a = JSON::Tiny::Actions.new();
     my $o = JSON::Tiny::Grammar.parse($text, :actions($a));

t/07-TO_JSON.t

@@ -0,0 +1,20 @@
+use v6;
+use Test;
+use JSON::Tiny;
+plan 2;
+
+class Something { 
+   has Str $.foo;
+   has Str $.bar;
+
+   method TO_JSON {
+      return {
+          foo => $.foo
+      }
+   }
+}
+
+my %something = from-json( to-json Something.new( foo => 'Interested', bar => 'Not interested' ) );
+
+is( %something<foo>, 'Interested', 'Include property' );
+isnt( %something<bar>, 'Not interested', 'Exclude property');