1 files changed, 36 insertions, 2 deletions
diff --git a/railties/guides/source/active_support_overview.textile b/railties/guides/source/active_support_overview.textile
index aea77c8d4e..4157694844 100644
--- a/railties/guides/source/active_support_overview.textile
+++ b/railties/guides/source/active_support_overview.textile
@@ -610,7 +610,23 @@ h3. Extensions to +FalseClass+
 
 h3. Extensions to +Symbol+
 
-...
+h4. +to_proc+
+
+The method +to_proc+ turns a symbol into a Proc object so that for example
+
+<ruby>
+emails = users.map {|u| u.email}
+</ruby>
+
+can be written as
+
+<ruby>
+emails = users.map(&:email)
+</ruby>
+
+TIP: If the method that receives the Proc yields more than one value to it the rest are considered to be arguments of the method call.
+
+Symbols from Ruby 1.8.7 on respond to +to_proc+, and Active Support defines it for previous versions.
 
 h3. Extensions to +String+
 
@@ -789,7 +805,25 @@ h3. Extensions to +Pathname+
 
 h3. Extensions to +File+
 
-...
+h4. +atomic_write+
+
+With the class method +File.atomic_write+ you can write to a file in a way that will prevent any reader from seeing half-written content.
+
+The name of the file is passed as an argument, and the method yields a file handle opened for writing. Once the block is done +atomic_write+ closes the file handle and completes its job.
+
+For example, Action Pack uses this method to write asset cache files like +all.css+:
+
+<ruby>
+File.atomic_write(joined_asset_path) do |cache|
+  cache.write(join_asset_file_contents(asset_paths))
+end
+</ruby>
+
+To accomplish this +atomic_write+ creates a temporary file. That's the file the code in the block actually writes to. On completion, the temporary file is renamed. If the target file exists +atomic_write+ overwrites it and keeps owners and permissions.
+
+WARNING. Note you can't append with +atomic_write+.
+
+The auxiliary file is written in a standard directory for temporary files, but you can pass a directory of your choice as second argument.
 
 h3. Extensions to +Exception+