From 857fcfa31dd5d69da533217a5bfd4a702b2b5a2b Mon Sep 17 00:00:00 2001
From: Simon Kornblith <simon@simonster.com>
Date: Wed, 14 Aug 2013 21:36:50 -0400
Subject: [PATCH] Add Zotero.lazy() and use in _getConnectionAsync

I tried to describe what this function does earlier today and failed.
Hopefully the code is clearer.
---
 chrome/content/zotero/xpcom/db.js     | 15 +++------------
 chrome/content/zotero/xpcom/zotero.js | 19 +++++++++++++++++++
 2 files changed, 22 insertions(+), 12 deletions(-)

diff --git a/chrome/content/zotero/xpcom/db.js b/chrome/content/zotero/xpcom/db.js
index 666ac7e084..1fb40ef929 100644
--- a/chrome/content/zotero/xpcom/db.js
+++ b/chrome/content/zotero/xpcom/db.js
@@ -70,7 +70,6 @@ Zotero.DBConnection = function(dbName) {
 	this._dbName = dbName;
 	this._shutdown = false;
 	this._connection = null;
-	this._connectionAsync = null;
 	this._transactionDate = null;
 	this._lastTransactionDate = null;
 	this._transactionRollback = false;
@@ -1021,23 +1020,15 @@ Zotero.DBConnection.prototype.asyncResult = function (val) {
 /**
  * Asynchronously return a connection object for the current DB
  */
-Zotero.DBConnection.prototype._getConnectionAsync = function () {
-	if (this._connectionAsync) {
-		return Q(this._connectionAsync);
-	}
-	
+Zotero.DBConnection.prototype._getConnectionAsync = Zotero.lazy(function() {
 	var db = this._getDBConnection();
 	var options = {
 		path: db.databaseFile.path
 	};
 	var self = this;
 	Zotero.debug("Asynchronously opening DB connection");
-	return Q(this.Sqlite.openConnection(options)
-	.then(function(conn) {
-		self._connectionAsync = conn;
-		return conn;
-	}));
-};
+	return Q(this.Sqlite.openConnection(options));
+});
 
 
 /*
diff --git a/chrome/content/zotero/xpcom/zotero.js b/chrome/content/zotero/xpcom/zotero.js
index 06a00ddc51..aa80c47a52 100644
--- a/chrome/content/zotero/xpcom/zotero.js
+++ b/chrome/content/zotero/xpcom/zotero.js
@@ -1518,6 +1518,25 @@ Components.utils.import("resource://gre/modules/Services.jsm");
 		return;
 	};
 	
+	/**
+	 * Generate a function that produces a static output
+	 *
+	 * Zotero.lazy(fn) returns a function. The first time this function
+	 * is called, it calls fn() and returns its output. Subsequent
+	 * calls return the same output as the first without calling fn()
+	 * again.
+	 */
+	this.lazy = function(fn) {
+		var x, called = false;
+		return function() {
+			if(!called) {
+				x = fn.apply(this);
+				called = true;
+			}
+			return x;
+		};
+	};
+	
 	/**
 	 * Pumps a generator until it yields false. See itemTreeView.js for an example.
 	 *