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.

Back after an unannounced absence

Hey everyone… I dropped the ball! A combination of unexpected family events, prepping for a conference, and some travel, meant I haven’t been writing for much longer than I like. But I’m back! So where were we? Oh that’s right… performance considerations with log/slog. We had looked at using the fmt.Stringer interface to avoid eager processing with slog.TextHandler. But let’s now look at a more general solution: Performance considerations …

Lazy attribute evaluation for JSONHandler

As I was writing yesterday’s post, a portion of the GoDoc confused me. I’ve now spent over 3 hours with Claude trying to parse the prose grammatically, build test cases, and make general sense of it. I think I finally have… Here’s hoping! So, yesterday we saw how you can lazy-evaluate some values when using TextHandler. But the proposed solution (pass a fmt.Stringer rather than a literal string) has other, likely uninintended, consequences if you’re using JSONHandler:

Get daily content like this in your inbox!

Subscribe