Remove utils::Prefable in favour of guard::Guard

components/script/dom/bindings/guard.rs

@@ -0,0 +1,49 @@
+/* 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/. */
+
+//! Machinery to conditionally expose things.
+
+use util::prefs::get_pref;
+
+/// A container with a condition.
+pub struct Guard<T: Clone + Copy> {
+    condition: Condition,
+    value: T,
+}
+
+impl<T: Clone + Copy> Guard<T> {
+    /// Construct a new guarded value.
+    pub const fn new(condition: Condition, value: T) -> Self {
+        Guard {
+            condition: condition,
+            value: value,
+        }
+    }
+
+    /// Expose the value if the condition is satisfied.
+    pub fn expose(&self) -> Option<T> {
+        if self.condition.is_satisfied() {
+            Some(self.value)
+        } else {
+            None
+        }
+    }
+}
+
+/// A condition to expose things.
+pub enum Condition {
+    /// The condition is satisfied if the preference is set.
+    Pref(&'static str),
+    /// The condition is always satisfied.
+    Satisfied,
+}
+
+impl Condition {
+    fn is_satisfied(&self) -> bool {
+        match *self {
+            Condition::Pref(name) => get_pref(name).as_boolean().unwrap_or(false),
+            Condition::Satisfied => true,
+        }
+    }
+}