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Revise general explanation on type casting #1354

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Revise general explanation on type casting #1354

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f9a3ae7
Revise general explanation on type casting
jaehyun1ee Dec 3, 2024
23d59b6
Nit pass on cast explainer
jaehyun1ee Jan 21, 2025
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15 changes: 10 additions & 5 deletions p4-16/spec/P4-16-spec.adoc
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Original file line number Diff line number Diff line change
Expand Up @@ -3841,18 +3841,23 @@ Additionally, the maximum size of a variable-length bit-string can be determined
[#sec-casts]
=== Casts

P4 provides a limited set of casts between types. A cast is written
`(t) e`, where `t` is a type and `e` is an expression. Casts are only
permitted on base types and derived types introduced by `typedef`, `type`, and `enum`.
While this design is arguably more onerous for programmers, it has several benefits:
P4 provides a set of casts between types. A cast is written
`(t) e`, where `t` is a type and `e` is an expression. Casts in P4 are
permitted only under the conditions specified in section <<sec-explicit-casts>>
for explicit casts and section <<sec-implicit-casts>> for implicit casts.
By allowing casts only in limited scenarios, this restriction is more
onerous for programmers, but it also provides several benefits.
Comment on lines +3848 to +3849
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nitpick: maybe this would read more naturally:

Suggested change
By allowing casts only in limited scenarios, this restriction is more
onerous for programmers, but it also provides several benefits.
Allowing casts only in limited scenarios is more onerous for
programmers, but it also provides several benefits.


* It makes user intent unambiguous.
* It makes the costs associated with converting numeric values
explicit. Implementing certain casts involves sign extensions,
and thus can require significant computational resources on some targets.
* It reduces the number of cases that have to be considered in the P4
specification. Some targets may not support all casts.
specification.

Some targets may not support all casts.

[#sec-explicit-casts]
==== Explicit casts

The following casts are legal in P4:
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