From 5f838d36cc75b57fac847da56ef8fdd9b9462a7b Mon Sep 17 00:00:00 2001
From: Karchnu <karchnu@karchnu.fr>
Date: Tue, 10 Nov 2020 20:14:50 +0100
Subject: [PATCH] Compute the number of object properties to serialize.

---
 src/cbor/serializable.cr | 51 +++++++++++++++++++++++++++-------------
 1 file changed, 35 insertions(+), 16 deletions(-)

diff --git a/src/cbor/serializable.cr b/src/cbor/serializable.cr
index 7ebd7d2..77d0689 100644
--- a/src/cbor/serializable.cr
+++ b/src/cbor/serializable.cr
@@ -136,6 +136,7 @@ module CBOR
       end
 
       private def self.new_from_cbor_decoder(decoder : ::CBOR::Decoder)
+        # puts "self.new_from_cbor_decoder"
         instance = allocate
         instance.initialize(__decoder_for_cbor_serializable: decoder)
         GC.add_finalizer(instance) if instance.responds_to?(:finalize)
@@ -268,9 +269,27 @@ module CBOR
           {% end %}
         {% end %}
 
-        cbor.object do
-          {% for name, value in properties %}
+        # Compute the size of the final list of properties to serialize.
+        # This allows a more compact encoding, and a faster decoding.
+        nb_properties_to_serialize = 0
+        {% for name, value in properties %}
             _{{name}} = @{{name}}
+          {% unless value[:emit_null] %}
+            unless _{{name}}.nil?
+              nb_properties_to_serialize += 1
+            end
+          {% else %}
+            nb_properties_to_serialize += 1
+          {% end %} # macro unless value[:emit_null]
+        {% end %} # macro for properties
+
+
+
+        {% if properties.size > 0 %}
+          cbor.write_object_start nb_properties_to_serialize
+
+          {% for name, value in properties %}
+              _{{name}} = @{{name}}
 
             {% unless value[:emit_null] %}
               unless _{{name}}.nil?
@@ -279,23 +298,23 @@ module CBOR
               # Write the key of the map
               cbor.write({{value[:key]}})
 
-              {% if value[:converter] %}
-                if _{{name}}
-                  {{ value[:converter] }}.to_cbor(_{{name}}, cbor)
-                else
-                  cbor.write(nil, use_undefined: value[:nil_as_undefined])
-                end
-              {% else %}
-                _{{name}}.to_cbor(cbor)
-              {% end %}
+            {% if value[:converter] %}
+              if _{{name}}
+                {{ value[:converter] }}.to_cbor(_{{name}}, cbor)
+              else
+                cbor.write(nil, use_undefined: value[:nil_as_undefined])
+              end
+            {% else %} # macro if value[:converter]
+              _{{name}}.to_cbor(cbor)
+            {% end %} # macro if value[:converter]
 
             {% unless value[:emit_null] %}
-              end
-            {% end %}
-          {% end %}
+              end # unless _{{name}}.nil?
+            {% end %} # macro unless value[:emit_null]
+          {% end %} # macro for properties
           on_to_cbor(cbor)
-        end
-      {% end %}
+        {% end %} # macro if properties.size > 0
+      {% end %} # begin
     end
 
     module Unmapped