feat: implement builder for mi element (ident)

src/elements/mfrac.rs

@@ -68,7 +68,7 @@ where
 ///
 /// let frac = Frac::builder().num("1").denom("2").build();
 /// ```
-#[derive(Debug, Clone, PartialEq, Eq, PartialOrd, Ord)]
+#[derive(Debug, Default, Clone, PartialEq, Eq, PartialOrd, Ord)]
 pub struct FracBuilder<N, D> {
     num: Option<MathMl>,
     denom: Option<MathMl>,
@@ -77,17 +77,6 @@ pub struct FracBuilder<N, D> {
     _marker: PhantomData<(N, D)>,
 }
 
-impl Default for FracBuilder<Uninit, Uninit> {
-    fn default() -> Self {
-        Self {
-            num: None,
-            denom: None,
-            attr: Vec::default(),
-            _marker: Default::default(),
-        }
-    }
-}
-
 impl<N, D> FracBuilder<N, D> {
     /// Add or overwrite the numerator to the `mfrac` element.
     pub fn num(self, num: impl Into<MathMl>) -> FracBuilder<Init, D> {

src/elements/mi.rs

@@ -1,4 +1,9 @@
-use crate::attributes::Attribute;
+use std::marker::PhantomData;
+
+use crate::{
+    attributes::Attribute,
+    markers::{Init, Uninit},
+};
 
 /// An attribute of `mi` element. Either one of the global [`Attribute`]s, or `mathvariant`
 /// attribute.
@@ -24,6 +29,12 @@ pub struct Ident {
     attributes: Vec<IdentAttr>,
 }
 
+impl Ident {
+    pub fn builder() -> IdentBuilder<Uninit> {
+        IdentBuilder::default()
+    }
+}
+
 impl<T> From<T> for Ident
 where
     T: Into<String>,
@@ -35,3 +46,38 @@ where
         }
     }
 }
+
+#[derive(Debug, Default, Clone, PartialEq, Eq, PartialOrd, Ord)]
+pub struct IdentBuilder<T> {
+    ident: Option<String>,
+    attributes: Vec<IdentAttr>,
+    _marker: PhantomData<(T,)>,
+}
+
+impl<T> IdentBuilder<T> {
+    pub fn ident(self, ident: impl Into<String>) -> IdentBuilder<Uninit> {
+        IdentBuilder {
+            ident: Some(ident.into()),
+            attributes: self.attributes,
+            _marker: PhantomData,
+        }
+    }
+
+    pub fn attr<I, A>(mut self, attr: I) -> Self
+    where
+        I: IntoIterator<Item = A>,
+        A: Into<IdentAttr>,
+    {
+        self.attributes.extend(attr.into_iter().map(Into::into));
+        self
+    }
+}
+
+impl IdentBuilder<Init> {
+    pub fn build(self) -> Ident {
+        Ident {
+            ident: self.ident.expect("Content is guaranteed to be init."),
+            attributes: self.attributes,
+        }
+    }
+}