I really like how Rust lets You do low-level things like decide how many bits your numbers use, But you can only choose between 8, 16, 32, 64, and 128 bit numbers, A variable I am using has only four possible values, so how could I make it the equivalent to a u2?
It is not possible to address less than a byte using Rust. (Just like it is not possible to manipulate less than a byte on basically any modern computer architecture.)
Generally, if you want to semantically express a choice out of a number of possibilities, you should use an enum, which will be checked at compile time to only ever contain one of its specified variants.
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If you're willing to write out all the possible bit strings (so definitely not for "all even 64-bit numbers") then you can make those enum variants and get a custom validity invariant through that.
See this hack, for example:
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That example is from the core Library, right?
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