Introduce Finite<T: Float> for restricted values defined in WebIDL.

components/script/dom/bindings/num.rs

@@ -0,0 +1,43 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+//! The `Finite<T>` struct.
+
+use core::nonzero::Zeroable;
+use std::num::Float;
+use std::ops::Deref;
+
+/// Encapsulates the IDL restricted float type.
+#[derive(Clone,Eq,PartialEq)]
+#[jstraceable]
+pub struct Finite<T: Float>(T);
+
+unsafe impl<T: Float> Zeroable for Finite<T> {}
+
+impl<T: Float> Finite<T> {
+    /// Create a new `Finite<T: Float>` safely.
+    pub fn new(value: T) -> Option<Finite<T>> {
+        if value.is_finite() {
+            Some(Finite(value))
+        } else {
+            None
+        }
+    }
+
+    /// Create a new `Finite<T: Float>`.
+    #[inline]
+    pub fn wrap(value: T) -> Finite<T> {
+        assert!(value.is_finite(), "Finite<T> doesn't encapsulate unrestricted value.");
+        Finite(value)
+    }
+}
+
+impl<T: Float> Deref for Finite<T> {
+    type Target = T;
+
+    fn deref(&self) -> &T {
+        let &Finite(ref value) = self;
+        value
+    }
+}