TIL: Flutter deletes toString from many classes

filip · February 1, 2026, 1:44pm

toString() behaves differently between debug and release modes

opened 09:04PM - 30 Jan 26 UTC

closed 01:30PM - 01 Feb 26 UTC

closed-as-intended

This is the first time I'm seeing this, but: - In Flutter in debug mode, when h…aving a `Size` object and logging it (e.g. `log.info("display size: $size");`), I get what I expect: [that class's override of `toString`](https://github.com/flutter/flutter/blob/master/engine/src/flutter/lib/ui/geometry.dart#L615): - `display size: Size(1420.0, 799.0)`. - But now I'm looking at logs from Sentry and I'm getting this: - `display size: Instance of 'Size'` - which is not very helpful Is that expected? - Dart version: 3.10.4 (stable) - I see this on macOS and Windows (desktop Flutter apps)

So, for example, logging log.info("Screen size: $size") will print the size correctly in debug mode, but it will print Screen size: Instance of ‘Size’` in production. This just bit me hard.