Reason for limiting fixed-length types to have a constant width

[pataei]

I'm wondering why P4 spec forces bit<W> or int<W> in some places, such as when they're used as the underlying type of a serializable enum or as the element type of a header. Why doesn't it just require a compile-time-known expression instead of a constant?

Also, does the use of W in spec always indicate a constant?

[vgurevich]

@pataei -- compile-time-known expressions are supported as type widths as long as you enclose them in parentheses. See Section 7.1.6.2 in the spec.

[mihaibudiu]

it should be a compile-time known value in the spec.

[pataei]

To double check my understanding, as an example, so there isn't anywhere in P4 that allows only bit<4> and not bit<(2+2)>, right?

[mihaibudiu]

These two should be fully equivalent and can be used in the same contexts. See also #1213

[pataei]

Closing this after the merge.