From 0702ab1829188c23ccdceb54ff6ac6786ecdff52 Mon Sep 17 00:00:00 2001
From: Ignotus Peverell <igno.peverell@protonmail.com>
Date: Tue, 20 Dec 2016 17:29:35 -0800
Subject: [PATCH] Utility crate for things that don't fit anywhere else. Helper
 struct to emcapsulate one time initializations with a RefCell of an Option.

---
 util/Cargo.toml |  4 ++++
 util/src/lib.rs | 49 +++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 53 insertions(+)
 create mode 100644 util/Cargo.toml
 create mode 100644 util/src/lib.rs

diff --git a/util/Cargo.toml b/util/Cargo.toml
new file mode 100644
index 000000000..a21d5e340
--- /dev/null
+++ b/util/Cargo.toml
@@ -0,0 +1,4 @@
+[package]
+name = "grin_util"
+version = "0.1.0"
+authors = ["Ignotus Peverell <igno.peverell@protonmail.com>"]
diff --git a/util/src/lib.rs b/util/src/lib.rs
new file mode 100644
index 000000000..f8bb8d913
--- /dev/null
+++ b/util/src/lib.rs
@@ -0,0 +1,49 @@
+// Copyright 2016 The Grin Developers
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+/// Various low-level utilities that factor Rust patterns that are frequent
+/// within the grin codebase.
+
+use std::cell::{RefCell, Ref};
+#[allow(unused_imports)]
+use std::ops::Deref;
+
+// Encapsulation of a RefCell<Option<T>> for one-time initialization after
+// construction. This implementation will purposefully fail hard if not used
+// properly, for example if it's not initialized before being first used
+// (borrowed).
+pub struct OneTime<T> {
+    inner: RefCell<Option<T>>,
+}
+
+unsafe impl<T> Sync for OneTime<T> {}
+unsafe impl<T> Send for OneTime<T> {}
+
+impl<T> OneTime<T> {
+    /// Builds a new uninitialized OneTime.
+    pub fn new() -> OneTime<T> {
+        OneTime { inner: RefCell::new(None) }
+    }
+
+    /// Initializes the OneTime, should only be called once after construction.
+    pub fn init(&self, value: T) {
+        let mut inner_mut = self.inner.borrow_mut();
+        *inner_mut = Some(value);
+    }
+
+    /// Borrows the OneTime, should only be called after initialization.
+    pub fn borrow(&self) -> Ref<T> {
+        Ref::map(self.inner.borrow(), |o| o.as_ref().unwrap())
+    }
+}