From 82df2e15b955e9ae7ff0ea9a81f04f95e3307a0a Mon Sep 17 00:00:00 2001
From: Marc-Antoine Arnaud <marc-antoine.arnaud@luminvent.com>
Date: Tue, 6 Feb 2024 00:36:58 +0100
Subject: [PATCH] feat!: remove requirement to Default issue #175 #144

---
 examples/src/bbigras_namespace.rs            |  8 +-
 examples/src/boscop.rs                       | 26 +++---
 examples/src/ln_dom.rs                       | 10 +-
 examples/src/svd.rs                          | 12 +--
 yaserde/src/lib.rs                           |  4 +-
 yaserde/tests/default.rs                     |  2 +-
 yaserde/tests/deserializer.rs                | 97 ++++++++------------
 yaserde/tests/flatten.rs                     | 34 +++----
 yaserde/tests/namespace.rs                   |  7 +-
 yaserde/tests/option.rs                      | 42 ++++++++-
 yaserde_derive/src/de/build_default_value.rs | 22 +++--
 yaserde_derive/src/de/expand_struct.rs       | 85 +++++++++--------
 12 files changed, 190 insertions(+), 159 deletions(-)

diff --git a/examples/src/bbigras_namespace.rs b/examples/src/bbigras_namespace.rs
index 41ed061..3a24435 100644
--- a/examples/src/bbigras_namespace.rs
+++ b/examples/src/bbigras_namespace.rs
@@ -1,7 +1,7 @@
 // related to issue https://github.com/media-io/yaserde/issues/15
 use yaserde::*;
 
-#[derive(YaDeserialize, Default, Debug, PartialEq)]
+#[derive(YaDeserialize, Debug, PartialEq)]
 #[yaserde(
   prefix = "ss",
   namespace = "x: urn:schemas-microsoft-com:office:excel",
@@ -14,7 +14,7 @@ struct Workbook {
   worksheet: Worksheet,
 }
 
-#[derive(YaDeserialize, Default, Debug, PartialEq)]
+#[derive(YaDeserialize, Debug, PartialEq)]
 #[yaserde(
   prefix = "ss",
   namespace = "x: urn:schemas-microsoft-com:office:excel",
@@ -29,7 +29,7 @@ struct Worksheet {
   ws_name: String,
 }
 
-#[derive(YaDeserialize, Default, Debug, PartialEq)]
+#[derive(YaDeserialize, Debug, PartialEq)]
 #[yaserde(
   prefix = "ss",
   namespace = "x: urn:schemas-microsoft-com:office:excel",
@@ -57,7 +57,7 @@ struct Table {
   rows: Vec<Row>,
 }
 
-#[derive(YaDeserialize, Default, Debug, PartialEq)]
+#[derive(YaDeserialize, Debug, PartialEq)]
 #[yaserde(
   prefix = "ss",
   namespace = "x: urn:schemas-microsoft-com:office:excel",
diff --git a/examples/src/boscop.rs b/examples/src/boscop.rs
index cb94b05..474cbb2 100644
--- a/examples/src/boscop.rs
+++ b/examples/src/boscop.rs
@@ -1,7 +1,7 @@
 // related to issue https://github.com/media-io/yaserde/issues/3
 use yaserde::*;
 
-#[derive(Default, Debug, Clone, PartialEq, YaDeserialize)]
+#[derive(Debug, Clone, PartialEq, YaDeserialize)]
 #[yaserde(root = "layout")]
 pub struct Layout {
   #[yaserde(attribute)]
@@ -17,7 +17,7 @@ pub struct Layout {
   pub tabpage: Vec<Tabpage>,
 }
 
-#[derive(Default, Debug, Clone, PartialEq, YaDeserialize)]
+#[derive(Debug, Clone, PartialEq, YaDeserialize)]
 pub struct Tabpage {
   #[yaserde(attribute, rename = "name")]
   pub named: String,
@@ -48,7 +48,7 @@ pub struct Tabpage {
   pub control: Vec<Control>,
 }
 
-#[derive(Default, Debug, Clone, PartialEq, YaDeserialize)]
+#[derive(Debug, Clone, PartialEq, YaDeserialize)]
 pub struct Control {
   #[yaserde(attribute, rename = "name")]
   pub named: String,
@@ -63,27 +63,27 @@ pub struct Control {
   #[yaserde(attribute)]
   pub color: String,
   #[yaserde(attribute)]
-  pub scalef: f32,
+  pub scalef: Option<f32>,
   #[yaserde(attribute)]
-  pub scalet: f32,
+  pub scalet: Option<f32>,
   #[yaserde(attribute)]
-  pub local_off: bool,
+  pub local_off: Option<bool>,
   #[yaserde(attribute)]
-  pub sp: bool,
+  pub sp: Option<bool>,
   #[yaserde(attribute)]
-  pub sr: bool,
+  pub sr: Option<bool>,
   pub midi: Vec<Midi>,
   #[yaserde(attribute)]
-  pub response: String,
+  pub response: Option<String>,
   #[yaserde(attribute)]
-  pub inverted: String,
+  pub inverted: Option<String>,
   #[yaserde(attribute)]
-  pub centered: String,
+  pub centered: Option<String>,
   #[yaserde(attribute)]
-  pub norollover: String,
+  pub norollover: Option<String>,
 }
 
-#[derive(Default, Debug, Clone, PartialEq, YaDeserialize)]
+#[derive(Debug, Clone, PartialEq, YaDeserialize)]
 pub struct Midi {
   #[yaserde(attribute)]
   pub var: String,
diff --git a/examples/src/ln_dom.rs b/examples/src/ln_dom.rs
index a1adf3f..baf8154 100644
--- a/examples/src/ln_dom.rs
+++ b/examples/src/ln_dom.rs
@@ -1,7 +1,7 @@
 // related to issue https://github.com/media-io/yaserde/issues/11
 use yaserde::*;
 
-#[derive(YaDeserialize, Default, Debug, PartialEq)]
+#[derive(YaDeserialize, Debug, PartialEq)]
 #[yaserde(root = "DOMSymbolItem")]
 struct Level {
   #[yaserde(attribute)]
@@ -11,13 +11,13 @@ struct Level {
   timeline: Timeline,
 }
 
-#[derive(YaDeserialize, Default, Debug, PartialEq)]
+#[derive(YaDeserialize, Debug, PartialEq)]
 struct Timeline {
   #[yaserde(rename = "DOMTimeline")]
   timeline: DOMTimeline,
 }
 
-#[derive(YaDeserialize, Default, Debug, PartialEq)]
+#[derive(YaDeserialize, Debug, PartialEq)]
 struct DOMTimeline {
   #[yaserde(attribute, rename = "name")]
   named: String,
@@ -28,13 +28,13 @@ struct DOMTimeline {
   layers: Layers,
 }
 
-#[derive(YaDeserialize, Default, Debug, PartialEq)]
+#[derive(YaDeserialize, Debug, PartialEq)]
 struct Layers {
   #[yaserde(rename = "DOMLayer")]
   dom_layer: Vec<DOMLayer>,
 }
 
-#[derive(YaDeserialize, Default, Debug, PartialEq)]
+#[derive(YaDeserialize, Debug, PartialEq)]
 struct DOMLayer {
   #[yaserde(attribute, rename = "name")]
   named: String,
diff --git a/examples/src/svd.rs b/examples/src/svd.rs
index 74e951f..2a8d72b 100644
--- a/examples/src/svd.rs
+++ b/examples/src/svd.rs
@@ -1,6 +1,6 @@
 use yaserde::YaSerialize;
 
-#[derive(Default, PartialEq, Debug, YaSerialize)]
+#[derive(PartialEq, Debug, YaSerialize)]
 struct CpuDef {
   #[yaserde(child)]
   name: String,
@@ -18,7 +18,7 @@ struct CpuDef {
   vendorsystickconfig: bool,
 }
 
-#[derive(Default, PartialEq, Debug, YaSerialize)]
+#[derive(PartialEq, Debug, YaSerialize)]
 struct Field {
   name: String,
   #[yaserde(child)]
@@ -29,7 +29,7 @@ struct Field {
   access: String,
 }
 
-#[derive(Default, PartialEq, Debug, YaSerialize)]
+#[derive(PartialEq, Debug, YaSerialize)]
 struct Register {
   #[yaserde(child)]
   name: String,
@@ -49,7 +49,7 @@ struct Register {
   fields: Vec<Field>,
 }
 
-#[derive(Default, PartialEq, Debug, YaSerialize)]
+#[derive(PartialEq, Debug, YaSerialize)]
 struct Peripheral {
   #[yaserde(child)]
   name: String,
@@ -69,7 +69,7 @@ struct Peripheral {
   registers: Vec<Register>,
 }
 
-#[derive(Default, PartialEq, Debug, YaSerialize)]
+#[derive(PartialEq, Debug, YaSerialize)]
 struct DevAttrs {
   #[yaserde(child)]
   vendor: String,
@@ -103,7 +103,7 @@ struct DevAttrs {
   peripherals: Vec<Peripheral>,
 }
 
-#[derive(Default, PartialEq, Debug, YaSerialize)]
+#[derive(PartialEq, Debug, YaSerialize)]
 #[yaserde(rename = "device")]
 struct Device {
   #[yaserde(attribute)]
diff --git a/yaserde/src/lib.rs b/yaserde/src/lib.rs
index c1ad4b4..971ce48 100644
--- a/yaserde/src/lib.rs
+++ b/yaserde/src/lib.rs
@@ -16,7 +16,7 @@
 //!```rust
 //! use yaserde_derive::YaSerialize;
 //!
-//! #[derive(Default, PartialEq, Debug, YaSerialize)]
+//! #[derive(PartialEq, Debug, YaSerialize)]
 //! #[yaserde(rename = "device")]
 //! struct Device {
 //!   #[yaserde(attribute)]
@@ -29,7 +29,7 @@
 //!   attributes: DeviceAttributes
 //! }
 //!
-//! #[derive(Default, PartialEq, Debug, YaSerialize)]
+//! #[derive(PartialEq, Debug, YaSerialize)]
 //! struct DeviceAttributes {
 //!   #[yaserde(child)]
 //!   vendor: String,
diff --git a/yaserde/tests/default.rs b/yaserde/tests/default.rs
index 510e990..2ea9e75 100644
--- a/yaserde/tests/default.rs
+++ b/yaserde/tests/default.rs
@@ -125,7 +125,7 @@ fn module_inclusion() {
   init();
 
   mod module {
-    #[derive(Debug, Default, PartialEq, YaDeserialize, YaSerialize)]
+    #[derive(Debug, PartialEq, YaDeserialize, YaSerialize)]
     #[yaserde(rename = "module")]
     pub struct Module {
       #[yaserde(attribute)]
diff --git a/yaserde/tests/deserializer.rs b/yaserde/tests/deserializer.rs
index fbc8612..de218c6 100644
--- a/yaserde/tests/deserializer.rs
+++ b/yaserde/tests/deserializer.rs
@@ -115,7 +115,7 @@ fn de_multiple_segments() {
   init();
 
   mod other_mod {
-    #[derive(YaDeserialize, PartialEq, Debug, Default)]
+    #[derive(YaDeserialize, PartialEq, Debug)]
     pub struct Page {
       pub number: i32,
       pub text: String,
@@ -216,14 +216,6 @@ fn de_attributes() {
     subitem: String,
   }
 
-  impl Default for SubStruct {
-    fn default() -> SubStruct {
-      SubStruct {
-        subitem: "".to_string(),
-      }
-    }
-  }
-
   let content = "<base item=\"something\"><sub subitem=\"sub-something\"></sub></base>";
   convert_and_validate!(
     content,
@@ -246,7 +238,7 @@ fn de_attributes_custom_deserializer() {
 
     use xml::reader::XmlEvent;
 
-    #[derive(Debug, Default, PartialEq)]
+    #[derive(Debug, PartialEq)]
     pub struct Attributes {
       pub items: Vec<String>,
     }
@@ -274,7 +266,7 @@ fn de_attributes_custom_deserializer() {
     }
   }
 
-  #[derive(Default, YaDeserialize, PartialEq, Debug)]
+  #[derive(YaDeserialize, PartialEq, Debug)]
   pub struct Struct {
     #[yaserde(attribute)]
     attr_option_string: Option<String>,
@@ -318,7 +310,7 @@ fn de_attributes_complex() {
     }
   }
 
-  #[derive(Default, YaDeserialize, PartialEq, Debug)]
+  #[derive(YaDeserialize, PartialEq, Debug)]
   pub struct Struct {
     #[yaserde(attribute)]
     attr_option_string: Option<String>,
@@ -349,7 +341,7 @@ fn de_attributes_complex() {
 fn de_attributes_with_same_name_field() {
   init();
 
-  #[derive(Default, YaDeserialize, PartialEq, Debug)]
+  #[derive(YaDeserialize, PartialEq, Debug)]
   pub struct Struct {
     #[yaserde(attribute, rename = "content")]
     attribute: Option<String>,
@@ -406,14 +398,6 @@ fn de_rename() {
     subitem: String,
   }
 
-  impl Default for SubStruct {
-    fn default() -> SubStruct {
-      SubStruct {
-        subitem: "".to_string(),
-      }
-    }
-  }
-
   let content = "<base Item=\"something\"><sub sub_item=\"sub_something\"></sub><maj.min.bug>2.0.1</maj.min.bug></base>";
   convert_and_validate!(
     content,
@@ -450,15 +434,6 @@ fn de_text_content_with_attributes() {
     text: String,
   }
 
-  impl Default for SubStruct {
-    fn default() -> SubStruct {
-      SubStruct {
-        subitem: "".to_string(),
-        text: "".to_string(),
-      }
-    }
-  }
-
   let content =
     "<base Item=\"something\"><sub sub_item=\"sub_something\">text_content</sub></base>";
   convert_and_validate!(
@@ -525,16 +500,6 @@ fn de_enum() {
     blue: String,
   }
 
-  impl Default for RGBColor {
-    fn default() -> RGBColor {
-      RGBColor {
-        red: "0".to_string(),
-        green: "0".to_string(),
-        blue: "0".to_string(),
-      }
-    }
-  }
-
   let content =
     "<?xml version=\"1.0\" encoding=\"utf-8\"?><base><background>Black</background></base>";
   convert_and_validate!(
@@ -593,7 +558,7 @@ fn de_complex_enum() {
     background: Color,
   }
 
-  #[derive(YaDeserialize, PartialEq, Debug, Default)]
+  #[derive(YaDeserialize, PartialEq, Debug)]
   pub struct OtherStruct {
     fi: i32,
     se: i32,
@@ -824,7 +789,7 @@ fn de_name_issue_21() {
 fn de_custom() {
   init();
 
-  #[derive(Default, PartialEq, Debug, YaDeserialize)]
+  #[derive(PartialEq, Debug, YaDeserialize)]
   struct Date {
     #[yaserde(rename = "Year")]
     year: i32,
@@ -834,7 +799,7 @@ fn de_custom() {
     day: Day,
   }
 
-  #[derive(Default, PartialEq, Debug)]
+  #[derive(PartialEq, Debug)]
   struct Day {
     value: i32,
   }
@@ -883,7 +848,7 @@ fn de_custom() {
 fn de_subitem_issue_12() {
   init();
 
-  #[derive(Default, PartialEq, Debug, YaDeserialize)]
+  #[derive(PartialEq, Debug, YaDeserialize)]
   pub struct Struct {
     id: i32,
   }
@@ -906,12 +871,12 @@ fn de_subitem_issue_12() {
 fn de_subitem_issue_12_with_sub() {
   init();
 
-  #[derive(Default, PartialEq, Debug, YaDeserialize)]
+  #[derive(PartialEq, Debug, YaDeserialize)]
   pub struct SubStruct {
     id: i32,
   }
 
-  #[derive(Default, PartialEq, Debug, YaDeserialize)]
+  #[derive(PartialEq, Debug, YaDeserialize)]
   pub struct Struct {
     id: i32,
     #[yaserde(rename = "SubStruct")]
@@ -939,7 +904,7 @@ fn de_subitem_issue_12_with_sub() {
 fn de_subitem_issue_12_attributes() {
   init();
 
-  #[derive(Default, PartialEq, Debug, YaDeserialize)]
+  #[derive(PartialEq, Debug, YaDeserialize)]
   pub struct Struct {
     #[yaserde(attribute)]
     id: i32,
@@ -960,13 +925,13 @@ fn de_subitem_issue_12_attributes() {
 fn de_subitem_issue_12_attributes_with_sub() {
   init();
 
-  #[derive(Default, PartialEq, Debug, YaDeserialize)]
+  #[derive(PartialEq, Debug, YaDeserialize)]
   pub struct SubStruct {
     #[yaserde(attribute)]
     id: i32,
   }
 
-  #[derive(Default, PartialEq, Debug, YaDeserialize)]
+  #[derive(PartialEq, Debug, YaDeserialize)]
   pub struct Struct {
     #[yaserde(attribute)]
     id: i32,
@@ -994,17 +959,23 @@ fn de_subitem_issue_12_attributes_with_sub() {
 fn de_same_field_name_sub() {
   init();
 
-  #[derive(Default, PartialEq, Debug, YaDeserialize)]
+  #[derive(PartialEq, Debug, YaDeserialize)]
   pub struct SubStruct {
     sub: Option<i32>,
   }
 
-  #[derive(Default, PartialEq, Debug, YaDeserialize)]
+  #[derive(PartialEq, Debug, YaDeserialize)]
   pub struct Struct {
     sub: SubStruct,
   }
 
-  convert_and_validate!("<Struct><sub /></Struct>", Struct, Struct::default());
+  convert_and_validate!(
+    "<Struct><sub /></Struct>",
+    Struct,
+    Struct {
+      sub: SubStruct { sub: None }
+    }
+  );
 
   convert_and_validate!(
     "<Struct><sub><sub>42</sub></sub></Struct>",
@@ -1019,22 +990,28 @@ fn de_same_field_name_sub() {
 fn de_same_field_name_sub_sub() {
   init();
 
-  #[derive(Default, PartialEq, Debug, YaDeserialize)]
+  #[derive(PartialEq, Debug, YaDeserialize)]
   pub struct SubSubStruct {
     sub: i32,
   }
 
-  #[derive(Default, PartialEq, Debug, YaDeserialize)]
+  #[derive(PartialEq, Debug, YaDeserialize)]
   pub struct SubStruct {
     sub: Option<SubSubStruct>,
   }
 
-  #[derive(Default, PartialEq, Debug, YaDeserialize)]
+  #[derive(PartialEq, Debug, YaDeserialize)]
   pub struct Struct {
     sub: SubStruct,
   }
 
-  convert_and_validate!("<Struct><sub /></Struct>", Struct, Struct::default());
+  convert_and_validate!(
+    "<Struct><sub /></Struct>",
+    Struct,
+    Struct {
+      sub: SubStruct { sub: None }
+    }
+  );
 
   convert_and_validate!(
     "<Struct>
@@ -1059,7 +1036,7 @@ fn de_same_field_name_sub_sub() {
 fn de_same_field_name_but_some_other_fields_or_something() {
   init();
 
-  #[derive(Default, PartialEq, Debug, YaDeserialize, YaSerialize)]
+  #[derive(PartialEq, Debug, YaDeserialize, YaSerialize)]
   #[yaserde(rename = "foo")]
   pub struct FooOuter {
     pub other: bool,
@@ -1067,7 +1044,7 @@ fn de_same_field_name_but_some_other_fields_or_something() {
     pub foo: Option<FooInner>,
   }
 
-  #[derive(Default, PartialEq, Debug, YaDeserialize, YaSerialize)]
+  #[derive(PartialEq, Debug, YaDeserialize, YaSerialize)]
   pub struct FooInner {
     pub blah: bool,
   }
@@ -1103,7 +1080,7 @@ fn de_attribute_sequence() {
     Bar,
   }
 
-  #[derive(Default, Debug, PartialEq, YaDeserialize)]
+  #[derive(Debug, PartialEq, YaDeserialize)]
   pub struct Outer {
     #[yaserde(attribute, rename = "seq1")]
     seq1: Vec<i32>,
@@ -1130,7 +1107,7 @@ fn de_nested_macro_rules() {
 
   macro_rules! float_attrs {
     ($type:ty) => {
-      #[derive(Default, PartialEq, Debug, YaDeserialize)]
+      #[derive(PartialEq, Debug, YaDeserialize)]
       pub struct Outer {
         #[yaserde(attribute)]
         pub inner: Option<$type>,
diff --git a/yaserde/tests/flatten.rs b/yaserde/tests/flatten.rs
index 34f9c51..f1ffe51 100644
--- a/yaserde/tests/flatten.rs
+++ b/yaserde/tests/flatten.rs
@@ -11,7 +11,7 @@ fn init() {
 fn basic_flatten() {
   init();
 
-  #[derive(Default, PartialEq, Debug, YaDeserialize, YaSerialize)]
+  #[derive(PartialEq, Debug, YaDeserialize, YaSerialize)]
   struct DateTime {
     #[yaserde(flatten)]
     date: Date,
@@ -20,7 +20,7 @@ fn basic_flatten() {
     kind: DateKind,
   }
 
-  #[derive(Default, PartialEq, Debug, YaDeserialize, YaSerialize)]
+  #[derive(PartialEq, Debug, YaDeserialize, YaSerialize)]
   struct Date {
     year: i32,
     month: i32,
@@ -31,18 +31,18 @@ fn basic_flatten() {
     optional_extra: Option<OptionalExtra>,
   }
 
-  #[derive(Default, PartialEq, Debug, YaDeserialize, YaSerialize)]
+  #[derive(PartialEq, Debug, YaDeserialize, YaSerialize)]
   pub struct Extra {
     week: i32,
     century: i32,
   }
 
-  #[derive(Default, PartialEq, Debug, YaDeserialize, YaSerialize)]
+  #[derive(PartialEq, Debug, YaDeserialize, YaSerialize)]
   pub struct OptionalExtra {
     lunar_day: i32,
   }
 
-  #[derive(PartialEq, Debug, YaDeserialize, YaSerialize, Default)]
+  #[derive(Debug, Default, PartialEq, YaDeserialize, YaSerialize)]
   pub enum DateKind {
     #[yaserde(rename = "holidays")]
     Holidays(Vec<String>),
@@ -150,7 +150,7 @@ fn root_flatten_enum() {
 fn flatten_attribute() {
   init();
 
-  #[derive(Default, PartialEq, Debug, YaDeserialize, YaSerialize)]
+  #[derive(PartialEq, Debug, YaDeserialize, YaSerialize)]
   struct HtmlText {
     #[yaserde(flatten)]
     text_attributes: TextAttributes,
@@ -158,7 +158,7 @@ fn flatten_attribute() {
     display: String,
   }
 
-  #[derive(Default, PartialEq, Debug, YaDeserialize, YaSerialize)]
+  #[derive(PartialEq, Debug, YaDeserialize, YaSerialize)]
   struct TextAttributes {
     #[yaserde(attribute)]
     bold: bool,
@@ -166,7 +166,7 @@ fn flatten_attribute() {
     font: FontAttributes,
   }
 
-  #[derive(Default, PartialEq, Debug, YaDeserialize, YaSerialize)]
+  #[derive(PartialEq, Debug, YaDeserialize, YaSerialize)]
   #[yaserde(namespace = "ns: http://www.sample.com/ns/domain")]
   pub struct FontAttributes {
     #[yaserde(attribute, prefix = "ns")]
@@ -192,20 +192,20 @@ fn flatten_attribute() {
 fn flatten_attribute_and_child() {
   init();
 
-  #[derive(Default, PartialEq, Debug, YaDeserialize, YaSerialize)]
+  #[derive(PartialEq, Debug, YaDeserialize, YaSerialize)]
   struct Node {
     #[yaserde(flatten)]
     base: Base,
     value: StringValue,
   }
 
-  #[derive(Default, PartialEq, Debug, YaDeserialize, YaSerialize)]
+  #[derive(PartialEq, Debug, YaDeserialize, YaSerialize)]
   struct Base {
     #[yaserde(attribute)]
     id: String,
   }
 
-  #[derive(Default, PartialEq, Debug, YaDeserialize, YaSerialize)]
+  #[derive(PartialEq, Debug, YaDeserialize, YaSerialize)]
   struct StringValue {
     #[yaserde(text)]
     string: String,
@@ -230,14 +230,14 @@ fn flatten_attribute_and_child() {
 fn flatten_name_in_unknown_child() {
   init();
 
-  #[derive(Default, PartialEq, Debug, YaDeserialize, YaSerialize)]
+  #[derive(PartialEq, Debug, YaDeserialize, YaSerialize)]
   pub struct Node {
     #[yaserde(flatten)]
     base: Base,
     value: Value,
   }
 
-  #[derive(Default, PartialEq, Debug, YaDeserialize, YaSerialize)]
+  #[derive(PartialEq, Debug, YaDeserialize, YaSerialize)]
   struct Base {
     #[yaserde(attribute)]
     id: String,
@@ -248,15 +248,15 @@ fn flatten_name_in_unknown_child() {
     Foo(FooStruct),
   }
 
-  #[derive(Default, PartialEq, Debug, YaDeserialize, YaSerialize)]
-  struct FooStruct {}
-
   impl Default for Value {
     fn default() -> Self {
-      Self::Foo(FooStruct::default())
+      Self::Foo(FooStruct {})
     }
   }
 
+  #[derive(PartialEq, Debug, YaDeserialize, YaSerialize)]
+  struct FooStruct {}
+
   let model = Node {
     base: Base {
       id: "Foo".to_owned(),
diff --git a/yaserde/tests/namespace.rs b/yaserde/tests/namespace.rs
index 3c28aed..6996165 100644
--- a/yaserde/tests/namespace.rs
+++ b/yaserde/tests/namespace.rs
@@ -145,7 +145,7 @@ fn struct_sub_namespace_definition() {
 fn struct_namespace_nested() {
   init();
 
-  #[derive(Debug, Default, PartialEq, YaDeserialize, YaSerialize)]
+  #[derive(Debug, PartialEq, YaDeserialize, YaSerialize)]
   #[yaserde(prefix = "nsa", namespace = "nsa: http://www.sample.com/ns/a")]
   struct A {
     #[yaserde(prefix = "nsa")]
@@ -180,7 +180,7 @@ fn struct_namespace_nested() {
 fn struct_namespace_nested_defined_at_root() {
   init();
 
-  #[derive(Debug, Default, PartialEq, YaDeserialize, YaSerialize)]
+  #[derive(Debug, PartialEq, YaDeserialize, YaSerialize)]
   #[yaserde(prefix = "nsa", namespace = "nsa: http://www.sample.com/ns/a")]
   struct A {
     #[yaserde(prefix = "nsa")]
@@ -326,13 +326,12 @@ fn struct_default_namespace_via_attribute_with_prefix() {
 fn enum_namespace() {
   init();
 
-  #[derive(Debug, PartialEq, YaDeserialize, YaSerialize)]
+  #[derive(Debug, Default, PartialEq, YaDeserialize, YaSerialize)]
   #[yaserde(
     rename = "root",
     prefix = "ns",
     namespace = "ns: http://www.sample.com/ns/domain"
   )]
-  #[derive(Default)]
   pub enum XmlStruct {
     #[yaserde(prefix = "ns")]
     #[default]
diff --git a/yaserde/tests/option.rs b/yaserde/tests/option.rs
index 17fa1bd..2166f19 100644
--- a/yaserde/tests/option.rs
+++ b/yaserde/tests/option.rs
@@ -85,7 +85,7 @@ fn option_struct() {
     field: SubTest,
   }
 
-  #[derive(Debug, Default, PartialEq, YaDeserialize, YaSerialize)]
+  #[derive(Debug, PartialEq, YaDeserialize, YaSerialize)]
   struct SubTest {
     content: Option<String>,
   }
@@ -111,7 +111,7 @@ fn option_bool_no_crash_on_bad_input() {
     field: SubTest,
   }
 
-  #[derive(Debug, Default, PartialEq, YaDeserialize, YaSerialize)]
+  #[derive(Debug, PartialEq, YaDeserialize, YaSerialize)]
   struct SubTest {
     #[yaserde(attribute)]
     content: Option<bool>,
@@ -122,3 +122,41 @@ fn option_bool_no_crash_on_bad_input() {
 
   assert!(result.is_err());
 }
+
+#[cfg(test)]
+mod tests {
+  use super::*;
+  use yaserde::de::from_str;
+
+  #[derive(Debug, YaDeserialize, YaSerialize)]
+  pub struct Car {
+    #[yaserde(rename = "CarColor")]
+    color: String,
+    #[yaserde(rename = "CarBrand")]
+    brand: String,
+  }
+
+  #[derive(Debug, YaDeserialize, YaSerialize)]
+  pub struct Person {
+    #[yaserde(flatten)]
+    pub car: Option<Car>,
+  }
+
+  #[test]
+  fn deserialize_without_car() {
+    let person = r#"<?xml version="1.0" encoding="utf-8"?>
+      <Person>
+          <EyeColor>brown</EyeColor>
+          <Age>25</Age>
+          <HasHome>true</HasHome>
+          <HasGarden>false</HasGarden>
+      </Person>
+    "#;
+
+    let person: Person = from_str(person).unwrap();
+
+    let expected_person = Person { car: None };
+
+    assert_eq!(person.car.is_none(), expected_person.car.is_none());
+  }
+}
diff --git a/yaserde_derive/src/de/build_default_value.rs b/yaserde_derive/src/de/build_default_value.rs
index 3dcd0fb..0ad14e0 100644
--- a/yaserde_derive/src/de/build_default_value.rs
+++ b/yaserde_derive/src/de/build_default_value.rs
@@ -5,14 +5,24 @@ use quote::quote;
 pub fn build_default_value(
   field: &YaSerdeField,
   field_type: Option<TokenStream>,
-  value: TokenStream,
 ) -> Option<TokenStream> {
   let label = field.get_value_label();
 
-  let default_value = field
-    .get_default_function()
-    .map(|default_function| quote!(#default_function()))
-    .unwrap_or_else(|| quote!(#value));
+  let field_type = field_type
+    .map(|field_type| quote!(: Option::<#field_type>))
+    .unwrap_or_default();
+
+  Some(quote! {
+    #[allow(unused_mut)]
+    let mut #label #field_type = None;
+  })
+}
+
+pub fn build_default_vec_value(
+  field: &YaSerdeField,
+  field_type: Option<TokenStream>,
+) -> Option<TokenStream> {
+  let label = field.get_value_label();
 
   let field_type = field_type
     .map(|field_type| quote!(: #field_type))
@@ -20,6 +30,6 @@ pub fn build_default_value(
 
   Some(quote! {
     #[allow(unused_mut)]
-    let mut #label #field_type = #default_value;
+    let mut #label #field_type = vec![];
   })
 }
diff --git a/yaserde_derive/src/de/expand_struct.rs b/yaserde_derive/src/de/expand_struct.rs
index a33aeab..f002e5c 100644
--- a/yaserde_derive/src/de/expand_struct.rs
+++ b/yaserde_derive/src/de/expand_struct.rs
@@ -1,7 +1,5 @@
-use crate::{
-  common::{Field, YaSerdeAttribute, YaSerdeField},
-  de::build_default_value::build_default_value,
-};
+use super::build_default_value::{build_default_value, build_default_vec_value};
+use crate::common::{Field, YaSerdeAttribute, YaSerdeField};
 use proc_macro2::{Span, TokenStream};
 use quote::quote;
 use syn::{DataStruct, Ident};
@@ -24,38 +22,25 @@ pub fn parse(
     .iter()
     .map(|field| YaSerdeField::new(field.clone()))
     .filter_map(|field| match field.get_type() {
-      Field::FieldStruct { struct_name } => build_default_value(
-        &field,
-        Some(quote!(#struct_name)),
-        quote!(<#struct_name as ::std::default::Default>::default()),
-      ),
-      Field::FieldOption { .. } => {
-        build_default_value(&field, None, quote!(::std::option::Option::None))
-      }
+      Field::FieldStruct { struct_name } => build_default_value(&field, Some(quote!(#struct_name))),
+      Field::FieldOption { .. } => build_default_value(&field, None),
       Field::FieldVec { data_type } => match *data_type {
-        Field::FieldStruct { ref struct_name } => build_default_value(
-          &field,
-          Some(quote!(::std::vec::Vec<#struct_name>)),
-          quote!(::std::vec![]),
-        ),
+        Field::FieldStruct { ref struct_name } => {
+          build_default_vec_value(&field, Some(quote!(::std::vec::Vec<#struct_name>)))
+        }
         Field::FieldOption { .. } | Field::FieldVec { .. } => {
-          unimplemented!("Option or Vec nested in  Vec<>");
+          unimplemented!("Option or Vec nested in Vec<>");
         }
         simple_type => {
           let type_token: TokenStream = simple_type.into();
 
-          build_default_value(
-            &field,
-            Some(quote!(::std::vec::Vec<#type_token>)),
-            quote!(::std::vec![]),
-          )
+          build_default_vec_value(&field, Some(quote!(::std::vec::Vec<#type_token>)))
         }
       },
       simple_type => {
         let type_token: TokenStream = simple_type.into();
-        let value_builder = quote!(<#type_token as ::std::default::Default>::default());
 
-        build_default_value(&field, Some(type_token), value_builder)
+        build_default_value(&field, Some(type_token))
       }
     })
     .collect();
@@ -74,6 +59,9 @@ pub fn parse(
 
         let visitor_label = field.get_visitor_ident(Some(&struct_name));
 
+        let xml_opening = format!("<{struct_id}>");
+        let xml_closing = format!("</{struct_id}>");
+
         Some(quote! {
           #[allow(non_snake_case, non_camel_case_types)]
           struct #visitor_label;
@@ -84,7 +72,7 @@ pub fn parse(
               self,
               v: &str,
             ) -> ::std::result::Result<Self::Value, ::std::string::String> {
-              let content = "<".to_string() + #struct_id + ">" + v + "</" + #struct_id + ">";
+              let content = format!("{}{}{}", #xml_opening, v, #xml_closing);
               ::yaserde::de::from_str(&content)
             }
           }
@@ -185,12 +173,14 @@ pub fn parse(
       };
 
       match field.get_type() {
-        Field::FieldStruct { struct_name } => visit_struct(struct_name, quote! { = value }),
+        Field::FieldStruct { struct_name } => {
+          visit_struct(struct_name, quote! { = ::std::option::Option::Some(value) })
+        }
         Field::FieldOption { data_type } => {
           visit_sub(data_type, quote! { = ::std::option::Option::Some(value) })
         }
         Field::FieldVec { data_type } => visit_sub(data_type, quote! { .push(value) }),
-        simple_type => visit_simple(simple_type, quote! { = value }),
+        simple_type => visit_simple(simple_type, quote! { = ::std::option::Option::Some(value) }),
       }
     })
     .collect();
@@ -205,7 +195,7 @@ pub fn parse(
 
       match field.get_type() {
         Field::FieldStruct { .. } => quote! {
-          #value_label = ::yaserde::de::from_str(&unused_xml_elements)?;
+          #value_label = Some(::yaserde::de::from_str(&unused_xml_elements)?);
         },
         Field::FieldOption { data_type } => match *data_type {
           Field::FieldStruct { .. } => quote! {
@@ -258,7 +248,7 @@ pub fn parse(
         Some(quote! {
           for attr in attributes {
             if attr.name.local_name == #label_name {
-              #label = attr.value.to_owned();
+              #label = Some(attr.value.to_owned());
             }
           }
         })
@@ -304,8 +294,8 @@ pub fn parse(
             &visitor_label,
           ),
         },
-        Field::FieldStruct { struct_name } => visit_struct(struct_name, quote! { = value }),
-        simple_type => visit_simple(simple_type, quote! { = value }),
+        Field::FieldStruct { struct_name } => visit_struct(struct_name, quote! { = Some(value) }),
+        simple_type => visit_simple(simple_type, quote! { = Some(value) }),
       }
     })
     .collect();
@@ -318,15 +308,13 @@ pub fn parse(
       let label = field.get_value_label();
 
       let set_text = |action: &TokenStream| {
-        if field.is_text_content() {
-          Some(quote! { #label = #action; })
-        } else {
-          None
-        }
+        field
+          .is_text_content()
+          .then_some(quote! { #label = #action; })
       };
 
       match field.get_type() {
-        Field::FieldString => set_text(&quote! { text_content.to_owned() }),
+        Field::FieldString => set_text(&quote! { Some(text_content.to_owned()) }),
         Field::FieldOption { data_type } => match *data_type {
           Field::FieldString => set_text(
             &quote! { if text_content.is_empty() { None } else { Some(text_content.to_owned()) }},
@@ -350,7 +338,26 @@ pub fn parse(
       let label = &field.label();
       let value_label = field.get_value_label();
 
-      quote! { #label: #value_label, }
+      match field.get_type() {
+        Field::FieldOption { .. } | Field::FieldVec { .. } => {
+          quote! { #label: #value_label, }
+        }
+        _ => {
+          if let Some(default_function) = field.get_default_function() {
+            quote! { #label: #value_label.unwrap_or_else(|| #default_function()), }
+          } else {
+            let error = format!(
+              "{} is a required field",
+              label
+                .as_ref()
+                .map(|label| label.to_string())
+                .unwrap_or_default()
+            );
+
+            quote! { #label: #value_label.ok_or_else(|| #error.to_string())?, }
+          }
+        }
+      }
     })
     .collect();