Adds AsRef<[Element]> for Sequence, List, and SExp (#841)

Author: popematt

src/element/sequence.rs

@@ -131,6 +131,12 @@ impl AsRef<Sequence> for Sequence {
     }
 }
 
+impl AsRef<[Element]> for Sequence {
+    fn as_ref(&self) -> &[Element] {
+        self.elements.as_slice()
+    }
+}
+
 // This is more efficient than Sequence::new(), which will iterate over and convert each value to
 // an Element for better ergonomics.
 impl From<Vec<Element>> for Sequence {

src/types/list.rs

@@ -52,6 +52,12 @@ impl AsRef<Sequence> for List {
     }
 }
 
+impl AsRef<[Element]> for List {
+    fn as_ref(&self) -> &[Element] {
+        self.0.as_ref()
+    }
+}
+
 // Allows `for element in &list {...}` syntax
 impl<'a> IntoIterator for &'a List {
     type Item = &'a Element;

src/types/sexp.rs

@@ -52,6 +52,12 @@ impl AsRef<Sequence> for SExp {
     }
 }
 
+impl AsRef<[Element]> for SExp {
+    fn as_ref(&self) -> &[Element] {
+        self.0.as_ref()
+    }
+}
+
 // Allows `for element in &sexp {...}` syntax
 impl<'a> IntoIterator for &'a SExp {
     type Item = &'a Element;