Taffy 0.8 - Allow retrieving underlying size from tagged pointer.

[PPakalns]

What problem does this solve or what need does it fill?

Taffy 0.8 now uses tagged ptr:

The representation of many "size" types is now a tagged pointer than an enum. This is to enable calc().
The effected types are LengthPercentage, LengthPercentageAuto, Dimension, MinTrackSizingFunction, and
MaxTrackSizingFunction types.

To make integrations like egui_taffy to work, taffy::Style inspection sometimes is necessary and stored style parameters must be read and based on them decision are made.

Support retrieving original value from tagged ptr.

What solution would you like?

For example -> LengthPercentage could return LengthPercentageEnum which would contain only Length, Percentage cases.

We can assume that this will be used for simple use cases where value can not contain ptr, but just raw values. If value contains ptr, then program can panic.

What alternative(s) have you considered?

Currently do not have useful ideas for alternatives.

Additional context

[nicoburns]

Yeah, this makes sense. I will get around to this at some point, but if you wanted to have at implementing this yourself then I think it would be quite doable. I think ideally we would have:

• ExpandedLengthPercentage (an enum like Taffy used to use - with conversions in both directions)
• LengthPercentageTag (a plain enum of just the discriminant).

For each of LengthPercentage, LengthPercentageAuto, Dimension, MinTrackSizingFunction, MaxTrackSizingFunction

[nicoburns]

A note that inspecting the value is possible (albeit not that ergonomic) with the current API by using .into_raw() to get a CompactLength and then calling .tag() (and then value() or calc_value() as appropriate) on the CompactValue.