Move user-facing serialization interface out of trait

instant-xml-macros/src/lib.rs

@@ -49,7 +49,10 @@ pub fn to_xml(input: proc_macro::TokenStream) -> proc_macro::TokenStream {
 
     proc_macro::TokenStream::from(quote!(
         impl #generics ToXml for #ident #generics {
-            fn serialize<W: std::fmt::Write>(&self, serializer: &mut instant_xml::Serializer<W>) -> Result<(), instant_xml::Error> {
+            fn serialize<W: ::core::fmt::Write + ?::core::marker::Sized>(
+                &self,
+                serializer: &mut instant_xml::Serializer<W>,
+            ) -> Result<(), instant_xml::Error> {
                 let _ = serializer.consume_field_context();
                 let mut field_context = instant_xml::ser::FieldContext {
                     name: #root_name,

instant-xml/src/impls.rs

@@ -54,10 +54,10 @@ impl<'a, T> ToXml for DisplayToXml<'a, T>
 where
     T: fmt::Display,
 {
-    fn serialize<W>(&self, serializer: &mut Serializer<W>) -> Result<(), Error>
-    where
-        W: fmt::Write,
-    {
+    fn serialize<W: fmt::Write + ?Sized>(
+        &self,
+        serializer: &mut Serializer<W>,
+    ) -> Result<(), Error> {
         let field_context = match serializer.consume_field_context() {
             Some(field_context) => field_context,
             None => return Err(Error::UnexpectedValue),
@@ -80,7 +80,7 @@ where
 macro_rules! to_xml_for_number {
     ($typ:ty) => {
         impl ToXml for $typ {
-            fn serialize<W: fmt::Write>(
+            fn serialize<W: fmt::Write + ?Sized>(
                 &self,
                 serializer: &mut Serializer<W>,
             ) -> Result<(), Error> {
@@ -321,7 +321,10 @@ to_xml_for_number!(f32);
 to_xml_for_number!(f64);
 
 impl ToXml for bool {
-    fn serialize<W: fmt::Write>(&self, serializer: &mut Serializer<W>) -> Result<(), Error> {
+    fn serialize<W: fmt::Write + ?Sized>(
+        &self,
+        serializer: &mut Serializer<W>,
+    ) -> Result<(), Error> {
         let value = match self {
             true => "true",
             false => "false",
@@ -332,32 +335,47 @@ impl ToXml for bool {
 }
 
 impl ToXml for String {
-    fn serialize<W: fmt::Write>(&self, serializer: &mut Serializer<W>) -> Result<(), Error> {
+    fn serialize<W: fmt::Write + ?Sized>(
+        &self,
+        serializer: &mut Serializer<W>,
+    ) -> Result<(), Error> {
         DisplayToXml(&escape(self)?).serialize(serializer)
     }
 }
 
 impl ToXml for char {
-    fn serialize<W: fmt::Write>(&self, serializer: &mut Serializer<W>) -> Result<(), Error> {
+    fn serialize<W: fmt::Write + ?Sized>(
+        &self,
+        serializer: &mut Serializer<W>,
+    ) -> Result<(), Error> {
         let mut tmp = [0u8; 4];
         DisplayToXml(&escape(&*self.encode_utf8(&mut tmp))?).serialize(serializer)
     }
 }
 
 impl ToXml for &str {
-    fn serialize<W: fmt::Write>(&self, serializer: &mut Serializer<W>) -> Result<(), Error> {
+    fn serialize<W: fmt::Write + ?Sized>(
+        &self,
+        serializer: &mut Serializer<W>,
+    ) -> Result<(), Error> {
         DisplayToXml(&escape(self)?).serialize(serializer)
     }
 }
 
 impl ToXml for Cow<'_, str> {
-    fn serialize<W: fmt::Write>(&self, serializer: &mut Serializer<W>) -> Result<(), Error> {
+    fn serialize<W: fmt::Write + ?Sized>(
+        &self,
+        serializer: &mut Serializer<W>,
+    ) -> Result<(), Error> {
         DisplayToXml(&escape(self)?).serialize(serializer)
     }
 }
 
 impl<T: ToXml> ToXml for Option<T> {
-    fn serialize<W: fmt::Write>(&self, serializer: &mut Serializer<W>) -> Result<(), Error> {
+    fn serialize<W: fmt::Write + ?Sized>(
+        &self,
+        serializer: &mut Serializer<W>,
+    ) -> Result<(), Error> {
         match self {
             Some(v) => v.serialize(serializer),
             None => Ok(()),

instant-xml/src/lib.rs

@@ -13,14 +13,10 @@ pub mod ser;
 pub use ser::Serializer;
 
 pub trait ToXml {
-    fn to_xml(&self) -> Result<String, Error> {
-        let mut output = String::new();
-        let mut serializer = Serializer::new(&mut output);
-        self.serialize(&mut serializer)?;
-        Ok(output)
-    }
-
-    fn serialize<W: fmt::Write>(&self, serializer: &mut Serializer<W>) -> Result<(), Error>;
+    fn serialize<W: fmt::Write + ?Sized>(
+        &self,
+        serializer: &mut Serializer<W>,
+    ) -> Result<(), Error>;
 }
 
 pub enum FieldAttribute<'xml> {
@@ -45,6 +41,19 @@ pub fn from_str<'xml, T: FromXml<'xml>>(input: &'xml str) -> Result<T, Error> {
     T::deserialize(&mut Deserializer::new(input))
 }
 
+pub fn to_string(value: &(impl ToXml + ?Sized)) -> Result<String, Error> {
+    let mut output = String::new();
+    to_writer(value, &mut output)?;
+    Ok(output)
+}
+
+pub fn to_writer(
+    value: &(impl ToXml + ?Sized),
+    output: &mut (impl fmt::Write + ?Sized),
+) -> Result<(), Error> {
+    value.serialize(&mut Serializer::new(output))
+}
+
 pub enum Kind {
     Scalar,
     Element(Id<'static>),

instant-xml/src/ser.rs

@@ -3,7 +3,7 @@ use std::fmt::{self, Write};
 
 use super::{Error, FieldAttribute};
 
-pub struct Serializer<'xml, W: fmt::Write> {
+pub struct Serializer<'xml, W: fmt::Write + ?Sized> {
     // For parent namespaces the key is the namespace and the value is the prefix. We are adding to map
     // only if the namespaces do not exist, if it does exist then we are using an already defined parent prefix.
     #[doc(hidden)]
@@ -17,7 +17,7 @@ pub struct Serializer<'xml, W: fmt::Write> {
     next_field_context: Option<FieldContext<'xml>>,
 }
 
-impl<'xml, W: fmt::Write> Serializer<'xml, W> {
+impl<'xml, W: fmt::Write + ?Sized> Serializer<'xml, W> {
     pub fn new(output: &'xml mut W) -> Self {
         Self {
             parent_namespaces: HashMap::new(),

instant-xml/tests/entities.rs

@@ -2,7 +2,7 @@ use std::borrow::Cow;
 
 use similar_asserts::assert_eq;
 
-use instant_xml::{from_str, Error, FromXml, ToXml};
+use instant_xml::{from_str, to_string, Error, FromXml, ToXml};
 
 #[derive(Debug, PartialEq, Eq, FromXml, ToXml)]
 #[xml(ns("URI"))]
@@ -57,13 +57,11 @@ fn escape_back() {
 #[test]
 fn special_entities() {
     assert_eq!(
-        StructSpecialEntities{
+        to_string(&StructSpecialEntities{
             string: "&\"<>\'aa".to_string(),
             str: "&\"<>\'bb",
             cow: Cow::from("&\"<>\'cc"),
-        }
-        .to_xml()
-        .unwrap(),
-        "<StructSpecialEntities xmlns=\"URI\"><string>&amp;&quot;&lt;&gt;&apos;aa</string><str>&amp;&quot;&lt;&gt;&apos;bb</str><cow>&amp;&quot;&lt;&gt;&apos;cc</cow></StructSpecialEntities>"
+        }).unwrap(),
+        "<StructSpecialEntities xmlns=\"URI\"><string>&amp;&quot;&lt;&gt;&apos;aa</string><str>&amp;&quot;&lt;&gt;&apos;bb</str><cow>&amp;&quot;&lt;&gt;&apos;cc</cow></StructSpecialEntities>",
     );
 }

instant-xml/tests/ser-child-ns.rs

@@ -1,6 +1,6 @@
 use similar_asserts::assert_eq;
 
-use instant_xml::ToXml;
+use instant_xml::{to_string, ToXml};
 
 #[derive(Debug, Eq, PartialEq, ToXml)]
 #[xml(ns(dar = "BAZ", internal = "INTERNAL"))]
@@ -33,7 +33,7 @@ struct Nested {
 #[test]
 fn struct_child_namespaces() {
     assert_eq!(
-        StructChildNamespaces {
+        to_string(&StructChildNamespaces {
             different_child_namespace: NestedDifferentNamespace {
                 flag_parent_prefix: true,
                 flag_internal_prefix: false,
@@ -42,8 +42,7 @@ fn struct_child_namespaces() {
                 flag_parent_prefix: true,
                 flag_internal_prefix: false,
             },
-        }
-        .to_xml()
+        })
         .unwrap(),
         "<StructChildNamespaces xmlns=\"URI\" xmlns:bar=\"BAZ\" xmlns:foo=\"BAR\"><NestedDifferentNamespace xmlns=\"\" xmlns:internal=\"INTERNAL\"><bar:flag_parent_prefix>true</bar:flag_parent_prefix><internal:flag_internal_prefix>false</internal:flag_internal_prefix></NestedDifferentNamespace><Nested xmlns:internal=\"INTERNAL\"><bar:flag_parent_prefix>true</bar:flag_parent_prefix><internal:flag_internal_prefix>false</internal:flag_internal_prefix></Nested></StructChildNamespaces>"
     );

instant-xml/tests/ser-named.rs

@@ -1,6 +1,6 @@
 use similar_asserts::assert_eq;
 
-use instant_xml::ToXml;
+use instant_xml::{to_string, ToXml};
 
 #[derive(Debug, Eq, PartialEq, ToXml)]
 #[xml(ns(bar = "BAZ", foo = "BAR"))]
@@ -20,12 +20,11 @@ struct StructWithNamedFields {
 #[test]
 fn struct_with_named_fields() {
     assert_eq!(
-        StructWithNamedFields {
+        to_string(&StructWithNamedFields {
             flag: true,
             string: "test".to_string(),
             number: 1,
-        }
-        .to_xml()
+        })
         .unwrap(),
         "<StructWithNamedFields xmlns:bar=\"BAZ\" xmlns:foo=\"BAR\"><flag>true</flag><bar:string>test</bar:string><number xmlns=\"typo\">1</number></StructWithNamedFields>"
     );

instant-xml/tests/ser-nested.rs

@@ -1,6 +1,6 @@
 use similar_asserts::assert_eq;
 
-use instant_xml::ToXml;
+use instant_xml::{to_string, ToXml};
 
 #[derive(Debug, Eq, PartialEq, ToXml)]
 #[xml(ns("URI", dar = "BAZ", internal = "INTERNAL"))]
@@ -37,7 +37,7 @@ struct StructWithCustomField {
 #[test]
 fn struct_with_custom_field() {
     assert_eq!(
-        StructWithCustomField {
+        to_string(&StructWithCustomField {
             int_attribute: 42,
             flag_direct_namespace_same_the_same_as_prefix: true,
             flag_prefix: false,
@@ -46,8 +46,7 @@ fn struct_with_custom_field() {
                 flag_parent_prefix: true,
                 flag_internal_prefix: false,
             },
-        }
-        .to_xml()
+        })
         .unwrap(),
         "<StructWithCustomField xmlns=\"URI\" xmlns:bar=\"BAZ\" xmlns:foo=\"BAR\" int_attribute=\"42\"><flag_direct_namespace_same_the_same_as_prefix xmlns=\"BAZ\">true</flag_direct_namespace_same_the_same_as_prefix><bar:flag_prefix>false</bar:flag_prefix><flag_direct_namespace xmlns=\"DIFFERENT\">true</flag_direct_namespace><Nested xmlns:internal=\"INTERNAL\"><bar:flag_parent_prefix>true</bar:flag_parent_prefix><internal:flag_internal_prefix>false</internal:flag_internal_prefix></Nested></StructWithCustomField>"
     );

instant-xml/tests/ser-unit.rs

@@ -1,12 +1,12 @@
 use similar_asserts::assert_eq;
 
-use instant_xml::ToXml;
+use instant_xml::{to_string, ToXml};
 
 #[derive(Debug, Eq, PartialEq, ToXml)]
 struct Unit;
 
 #[test]
 fn unit() {
-    assert_eq!(Unit.to_xml().unwrap(), "<Unit></Unit>");
+    assert_eq!(to_string(&Unit).unwrap(), "<Unit></Unit>");
     //assert_eq!(Unit::from_xml("<Unit/>").unwrap(), Unit);
 }