Blog / Standard Library

Working with Records

May 18, 2026

In my experience, it’s rare you’ll need to worry about slog Records, unless you’re writing a Handler, or some kind of middleware/transform. But even if you never need to manipulate a Record directly, understanding the concept can be useful.

Working with Records

Sometimes a Handler will need to modify a Record before passing it on to another Handler or backend. A Record contains a mixture of simple public fields (e.g. Time, Level, Message) and hidden fields that refer to state (such as attributes) indirectly. This means that modifying a simple copy of a Record (e.g. by calling Record.Add or Record.AddAttrs to add attributes) may have unexpected effects on the original. Before modifying a Record, use Record.Clone to create a copy that shares no state with the original, or create a new Record with NewRecord and build up its Attrs by traversing the old ones with Record.Attrs.

TL;DR; don’t copy records! Clone them, either direction (Record.Clone) or indeirectly!

We’ll look into the nitty gritty details of Records later on.

Share this

Direct to your inbox, daily. I respect your privacy .

Unsure? Browse the archive .

Related Content

slog Records and levels

Yesterday we saw that slog uses handlers to process/record logs. But what exactly does it process? Records! Overview … A log record consists of a time, a level, a message, and a set of key-value pairs, where the keys are strings and the values may be of any type. As an example, slog.Info("hello", "count", 3) creates a record containing the time of the call, a level of Info, the message “hello”, and a single pair with key “count” and value 3.

slog.Handler

I’m probably doing this in backwards order, but that’s the order the GoDoc presents it… Now that we’ve looked at each of the methods of the Handler interface, we come to its general description: type Handler A Handler handles log records produced by a Logger. A typical handler may print log records to standard error, or write them to a file or database, or perhaps augment them with additional attributes and pass them on to another handler.

slog.Handler.WithGroup

I hope everyone had a good Labor Day weekend… even if you’re not in the US and had to/got to labor on Monday. Speaking of labor, I’m looking for new clients! If you could use some world class Go expertise on your project, please reach out! type Handler type Handler interface { … // WithGroup returns a new Handler with the given group appended to // the receiver's existing groups. // The keys of all subsequent attributes, whether added by With or in a // Record, should be qualified by the sequence of group names.

Get daily content like this in your inbox!

Subscribe