Change default parameter of Cast

src/eval/func.rs

@@ -171,7 +171,10 @@ impl Args {
     ///
     /// Returns a `missing argument: {what}` error if no positional argument is
     /// left.
-    pub fn expect<T: Cast>(&mut self, what: &str) -> TypResult<T> {
+    pub fn expect<T>(&mut self, what: &str) -> TypResult<T>
+    where
+        T: Cast<Spanned<Value>>,
+    {
         match self.eat()? {
             Some(v) => Ok(v),
             None => bail!(self.span, "missing argument: {}", what),
@@ -179,7 +182,10 @@ impl Args {
     }
 
     /// Consume and cast the first positional argument if there is one.
-    pub fn eat<T: Cast>(&mut self) -> TypResult<Option<T>> {
+    pub fn eat<T>(&mut self) -> TypResult<Option<T>>
+    where
+        T: Cast<Spanned<Value>>,
+    {
         for (i, slot) in self.items.iter().enumerate() {
             if slot.name.is_none() {
                 let value = self.items.remove(i).value;
@@ -191,7 +197,10 @@ impl Args {
     }
 
     /// Find and consume the first castable positional argument.
-    pub fn find<T: Cast>(&mut self) -> TypResult<Option<T>> {
+    pub fn find<T>(&mut self) -> TypResult<Option<T>>
+    where
+        T: Cast<Spanned<Value>>,
+    {
         for (i, slot) in self.items.iter().enumerate() {
             if slot.name.is_none() && T::is(&slot.value) {
                 let value = self.items.remove(i).value;
@@ -203,7 +212,10 @@ impl Args {
     }
 
     /// Find and consume all castable positional arguments.
-    pub fn all<T: Cast>(&mut self) -> TypResult<Vec<T>> {
+    pub fn all<T>(&mut self) -> TypResult<Vec<T>>
+    where
+        T: Cast<Spanned<Value>>,
+    {
         let mut list = vec![];
         while let Some(value) = self.find()? {
             list.push(value);
@@ -213,7 +225,10 @@ impl Args {
 
     /// Cast and remove the value for the given named argument, returning an
     /// error if the conversion fails.
-    pub fn named<T: Cast>(&mut self, name: &str) -> TypResult<Option<T>> {
+    pub fn named<T>(&mut self, name: &str) -> TypResult<Option<T>>
+    where
+        T: Cast<Spanned<Value>>,
+    {
         // We don't quit once we have a match because when multiple matches
         // exist, we want to remove all of them and use the last one.
         let mut i = 0;
@@ -231,7 +246,10 @@ impl Args {
     }
 
     /// Same as named, but with fallback to find.
-    pub fn named_or_find<T: Cast>(&mut self, name: &str) -> TypResult<Option<T>> {
+    pub fn named_or_find<T>(&mut self, name: &str) -> TypResult<Option<T>>
+    where
+        T: Cast<Spanned<Value>>,
+    {
         match self.named(name)? {
             Some(value) => Ok(Some(value)),
             None => self.find(),
@@ -266,10 +284,7 @@ impl Args {
     }
 
     /// Reinterpret these arguments as actually being a single castable thing.
-    fn into_castable<T>(self, what: &str) -> TypResult<T>
+    fn into_castable<T: Cast>(self, what: &str) -> TypResult<T> {
-    where
-        T: Cast<Value>,
-    {
         let mut iter = self.items.into_iter();
         let value = match iter.next() {
             Some(Arg { name: None, value, .. }) => value.v.cast().at(value.span)?,

src/eval/value.rs

@@ -97,10 +97,7 @@ impl Value {
     }
 
     /// Try to cast the value into a specific type.
-    pub fn cast<T>(self) -> StrResult<T>
+    pub fn cast<T: Cast>(self) -> StrResult<T> {
-    where
-        T: Cast<Value>,
-    {
         T::cast(self)
     }
 
@@ -327,7 +324,7 @@ pub trait Type {
 }
 
 /// Cast from a value to a specific type.
-pub trait Cast<V = Spanned<Value>>: Sized {
+pub trait Cast<V = Value>: Sized {
     /// Check whether the value is castable to `Self`.
     fn is(value: &V) -> bool;
 
@@ -345,7 +342,7 @@ macro_rules! primitive {
             const TYPE_NAME: &'static str = $name;
         }
 
-        impl Cast<Value> for $type {
+        impl Cast for $type {
             fn is(value: &Value) -> bool {
                 matches!(value, Value::$variant(_) $(| Value::$other(_))*)
             }
@@ -448,7 +445,7 @@ primitive! { Func: "function", Func, Class(v) => v.constructor() }
 primitive! { Args: "arguments", Args }
 primitive! { Class: "class", Class }
 
-impl Cast<Value> for Value {
+impl Cast for Value {
     fn is(_: &Value) -> bool {
         true
     }
@@ -458,10 +455,7 @@ impl Cast<Value> for Value {
     }
 }
 
-impl<T> Cast for T
+impl<T: Cast> Cast<Spanned<Value>> for T {
-where
-    T: Cast<Value>,
-{
     fn is(value: &Spanned<Value>) -> bool {
         T::is(&value.v)
     }
@@ -471,10 +465,7 @@ where
     }
 }
 
-impl<T> Cast for Spanned<T>
+impl<T: Cast> Cast<Spanned<Value>> for Spanned<T> {
-where
-    T: Cast<Value>,
-{
     fn is(value: &Spanned<Value>) -> bool {
         T::is(&value.v)
     }
@@ -511,10 +502,7 @@ impl<T> Default for Smart<T> {
     }
 }
 
-impl<T> Cast<Value> for Option<T>
+impl<T: Cast> Cast for Option<T> {
-where
-    T: Cast<Value>,
-{
     fn is(value: &Value) -> bool {
         matches!(value, Value::None) || T::is(value)
     }
@@ -527,10 +515,7 @@ where
     }
 }
 
-impl<T> Cast<Value> for Smart<T>
+impl<T: Cast> Cast for Smart<T> {
-where
-    T: Cast<Value>,
-{
     fn is(value: &Value) -> bool {
         matches!(value, Value::Auto) || T::is(value)
     }