Pass arguments to call and construct directly by value

3 files changed, 38 insertions, 37 deletions

diff --git a/src/eval/class.rs b/src/eval/class.rs
index 4307eecb..acdf38e6 100644
--- a/src/eval/class.rs
+++ b/src/eval/class.rs
@@ -6,15 +6,15 @@ use crate::diag::TypResult;
 /// A class of nodes.
 ///
 /// You can [construct] an instance of a class in Typst code by invoking the
-/// class as a callable. This always produces a template, but not necessarily a
-/// simple inline or block node. For example, the `text` constructor does not
-/// actually create a [`TextNode`]. Instead it applies styling to whatever node
-/// you pass in and returns it structurally unchanged.
+/// class as a callable. This always produces a template value, but not
+/// necessarily a simple inline or block node. For example, the `text`
+/// constructor does not actually create a [`TextNode`]. Instead it applies
+/// styling to whatever node you pass in and returns it structurally unchanged.
 ///
 /// The arguments you can pass to a class constructor fall into two categories:
-/// Data that is inherent to the instance (e.g. the text of a heading) and style
-/// properties (e.g. the fill color of a heading). As the latter are often
-/// shared by many instances throughout a document, they can also be
+/// Data that is inherent to the instance (e.g. the text/content of a heading)
+/// and style properties (e.g. the fill color of a heading). As the latter are
+/// often shared by many instances throughout a document, they can also be
 /// conveniently configured through class's [`set`] rule. Then, they apply to
 /// all nodes that are instantiated into the template where the `set` was
 /// executed.
@@ -62,25 +62,30 @@ impl Class {
         self.name
     }
 
+    /// Return the class constructor as a function.
+    pub fn constructor(&self) -> Func {
+        Func::native(self.name, self.construct)
+    }
+
     /// Construct an instance of the class.
     ///
-    /// This parses both property and data arguments (in this order) and styles
-    /// the template constructed from the data with the style properties.
-    pub fn construct(&self, ctx: &mut EvalContext, args: &mut Args) -> TypResult<Value> {
-        (self.construct)(ctx, args)
+    /// This parses both property and data arguments (in this order), styles the
+    /// template constructed from the data with the style properties and wraps
+    /// it in a value.
+    pub fn construct(&self, ctx: &mut EvalContext, mut args: Args) -> TypResult<Value> {
+        let value = (self.construct)(ctx, &mut args)?;
+        args.finish()?;
+        Ok(value)
     }
 
     /// Execute the class's set rule.
     ///
-    /// This parses property arguments and writes the resulting styles into the
-    /// given style map. There are no further side effects.
-    pub fn set(&self, args: &mut Args, styles: &mut StyleMap) -> TypResult<()> {
-        (self.set)(args, styles)
-    }
-
-    /// Return the class constructor as a function.
-    pub fn constructor(&self) -> Func {
-        Func::native(self.name, self.construct)
+    /// This parses property arguments and return the resulting styles.
+    pub fn set(&self, mut args: Args) -> TypResult<StyleMap> {
+        let mut styles = StyleMap::new();
+        (self.set)(&mut args, &mut styles)?;
+        args.finish()?;
+        Ok(styles)
     }
 }
 
diff --git a/src/eval/func.rs b/src/eval/func.rs
index ccd0932f..6d405ca4 100644
--- a/src/eval/func.rs
+++ b/src/eval/func.rs
@@ -45,15 +45,17 @@ impl Func {
     }
 
     /// Call the function in the context with the arguments.
-    pub fn call(&self, ctx: &mut EvalContext, args: &mut Args) -> TypResult<Value> {
-        match self.0.as_ref() {
-            Repr::Native(native) => (native.func)(ctx, args),
-            Repr::Closure(closure) => closure.call(ctx, args),
+    pub fn call(&self, ctx: &mut EvalContext, mut args: Args) -> TypResult<Value> {
+        let value = match self.0.as_ref() {
+            Repr::Native(native) => (native.func)(ctx, &mut args)?,
+            Repr::Closure(closure) => closure.call(ctx, &mut args)?,
             Repr::With(wrapped, applied) => {
                 args.items.splice(.. 0, applied.items.iter().cloned());
-                wrapped.call(ctx, args)
+                return wrapped.call(ctx, args);
             }
-        }
+        };
+        args.finish()?;
+        Ok(value)
     }
 
     /// Apply the given arguments to the function.
diff --git a/src/eval/mod.rs b/src/eval/mod.rs
index 33ee23ca..7c038c2a 100644
--- a/src/eval/mod.rs
+++ b/src/eval/mod.rs
@@ -189,10 +189,8 @@ fn eval_markup(
             MarkupNode::Expr(Expr::Set(set)) => {
                 let class = set.class();
                 let class = class.eval(ctx)?.cast::<Class>().at(class.span())?;
-                let mut args = set.args().eval(ctx)?;
-                let mut styles = StyleMap::new();
-                class.set(&mut args, &mut styles)?;
-                args.finish()?;
+                let args = set.args().eval(ctx)?;
+                let styles = class.set(args)?;
                 let tail = eval_markup(ctx, nodes)?;
                 tail.styled_with_map(styles)
             }
@@ -590,7 +588,7 @@ impl Eval for CallExpr {
     fn eval(&self, ctx: &mut EvalContext) -> TypResult<Self::Output> {
         let span = self.callee().span();
         let callee = self.callee().eval(ctx)?;
-        let mut args = self.args().eval(ctx)?;
+        let args = self.args().eval(ctx)?;
 
         match callee {
             Value::Array(array) => {
@@ -603,16 +601,12 @@ impl Eval for CallExpr {
 
             Value::Func(func) => {
                 let point = || Tracepoint::Call(func.name().map(ToString::to_string));
-                let value = func.call(ctx, &mut args).trace(point, self.span())?;
-                args.finish()?;
-                Ok(value)
+                func.call(ctx, args).trace(point, self.span())
             }
 
             Value::Class(class) => {
                 let point = || Tracepoint::Call(Some(class.name().to_string()));
-                let value = class.construct(ctx, &mut args).trace(point, self.span())?;
-                args.finish()?;
-                Ok(value)
+                class.construct(ctx, args).trace(point, self.span())
             }
 
             v => bail!(