Clarify FromXml identity const

instant-xml-macros/src/de.rs

@@ -218,7 +218,7 @@ impl Deserializer {
         ));
 
         out.extend(quote!(
-            const TAG_NAME: ::instant_xml::TagName = ::instant_xml::TagName::Custom(#name);
+            const KIND: ::instant_xml::Kind = ::instant_xml::Kind::Element(#name);
         ));
 
         out = quote!(
@@ -251,10 +251,7 @@ impl Deserializer {
         tokens.enum_.extend(quote!(#enum_name,));
 
         tokens.consts.extend(quote!(
-            const #const_field_var_str: &str = match <#no_lifetime_type>::TAG_NAME {
-                ::instant_xml::TagName::FieldName => #field_var_str,
-                ::instant_xml::TagName::Custom(v) => v,
-            };
+            const #const_field_var_str: &str = <#no_lifetime_type>::KIND.name(#field_var_str);
         ));
 
         if is_element {

instant-xml/src/impls.rs

@@ -4,7 +4,7 @@ use std::marker::PhantomData;
 use std::str::FromStr;
 
 use crate::de::{EntityType, Visitor};
-use crate::{Deserializer, Error, FieldAttribute, FromXml, Serializer, TagName, ToXml};
+use crate::{Deserializer, Error, FieldAttribute, FromXml, Kind, Serializer, ToXml};
 
 // Deserializer
 struct FromStrToVisitor<T: FromStr>(PhantomData<T>)
@@ -37,7 +37,7 @@ impl<'xml> Visitor<'xml> for BoolVisitor {
 }
 
 impl<'xml> FromXml<'xml> for bool {
-    const TAG_NAME: TagName = TagName::FieldName;
+    const KIND: Kind = Kind::Scalar;
 
     fn deserialize(deserializer: &mut Deserializer) -> Result<Self, Error> {
         match deserializer.consume_next_type() {
@@ -113,8 +113,6 @@ where
 macro_rules! from_xml_for_number {
     ($typ:ty) => {
         impl<'xml> FromXml<'xml> for $typ {
-            const TAG_NAME: TagName = TagName::FieldName;
-
             fn deserialize(deserializer: &mut Deserializer) -> Result<Self, Error> {
                 match deserializer.consume_next_type() {
                     EntityType::Element => deserializer.deserialize_element(NumberVisitor {
@@ -125,6 +123,8 @@ macro_rules! from_xml_for_number {
                     }),
                 }
             }
+
+            const KIND: Kind = Kind::Scalar;
         }
     };
 }
@@ -153,7 +153,7 @@ impl<'xml> Visitor<'xml> for StringVisitor {
 }
 
 impl<'xml> FromXml<'xml> for String {
-    const TAG_NAME: TagName = TagName::FieldName;
+    const KIND: Kind = Kind::Scalar;
 
     fn deserialize(deserializer: &mut Deserializer) -> Result<Self, Error> {
         //<&'xml str>::deserialize(deserializer);
@@ -178,7 +178,7 @@ impl<'xml> Visitor<'xml> for CharVisitor {
 }
 
 impl<'xml> FromXml<'xml> for char {
-    const TAG_NAME: TagName = TagName::FieldName;
+    const KIND: Kind = Kind::Scalar;
 
     fn deserialize(deserializer: &mut Deserializer) -> Result<Self, Error> {
         match deserializer.consume_next_type() {
@@ -202,7 +202,7 @@ impl<'a> Visitor<'a> for StrVisitor {
 }
 
 impl<'xml> FromXml<'xml> for &'xml str {
-    const TAG_NAME: TagName = TagName::FieldName;
+    const KIND: Kind = Kind::Scalar;
 
     fn deserialize(deserializer: &mut Deserializer<'xml>) -> Result<Self, Error> {
         match deserializer.consume_next_type() {
@@ -223,7 +223,7 @@ impl<'a> Visitor<'a> for CowStrVisitor {
 }
 
 impl<'xml> FromXml<'xml> for Cow<'xml, str> {
-    const TAG_NAME: TagName = <&str>::TAG_NAME;
+    const KIND: Kind = <&str>::KIND;
 
     fn deserialize(deserializer: &mut Deserializer<'xml>) -> Result<Self, Error> {
         match deserializer.consume_next_type() {
@@ -237,7 +237,7 @@ impl<'xml, T> FromXml<'xml> for Option<T>
 where
     T: FromXml<'xml>,
 {
-    const TAG_NAME: TagName = <T>::TAG_NAME;
+    const KIND: Kind = <T>::KIND;
 
     fn deserialize(deserializer: &mut Deserializer<'xml>) -> Result<Self, Error> {
         match <T>::deserialize(deserializer) {

instant-xml/src/lib.rs

@@ -29,14 +29,7 @@ pub enum FieldAttribute<'xml> {
     Attribute,
 }
 
-pub enum TagName {
-    FieldName,
-    Custom(&'static str),
-}
-
 pub trait FromXml<'xml>: Sized {
-    const TAG_NAME: TagName;
-
     fn from_xml(input: &'xml str) -> Result<Self, Error> {
         let mut deserializer = Deserializer::new(input);
         Self::deserialize(&mut deserializer)
@@ -49,6 +42,22 @@ pub trait FromXml<'xml>: Sized {
     fn missing_value() -> Result<Self, Error> {
         Err(Error::MissingValue)
     }
+
+    const KIND: Kind;
+}
+
+pub enum Kind {
+    Scalar,
+    Element(&'static str),
+}
+
+impl Kind {
+    pub const fn name(&self, field: &'static str) -> &'static str {
+        match self {
+            Kind::Scalar => field,
+            Kind::Element(name) => name,
+        }
+    }
 }
 
 pub trait FromXmlOwned: for<'xml> FromXml<'xml> {}