Allow concatenation of string literals at compile time #1299
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vlstill
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Resulting PDF spec P4-16-spec.pdf. |
Signed-off-by: Vladimir Still <[email protected]>
Signed-off-by: Vladimír Štill <[email protected]>
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@jafingerhut, @jonathan-dilorenzo, @rcgoodfellow, any comments? I'd love for this one to get in before the next spec revision goes out. |
p4-16/spec/P4-16-spec.mdk
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| deprecated construct. This is mostly useful for annotating library | ||
| constructs, such as externs. | ||
| deprecated construct. This is mostly useful for annotating library | ||
| constructs, such as externs. The parameter needs to be local |
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nit: needs to be local -> needs to be a local
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Would also go with 'must be' over 'needs to be' imo.
p4-16/spec/P4-16-spec.mdk
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| @@ -8602,7 8627,8 @@ extern Checker { | |||
| The `noWarn` annotation has a required string argument that indicates | |||
| a compiler warning that will be inhibited. For example | |||
| `@noWarn("unused")` on a declaration will prevent a compiler warning | |||
| if that declaration is not used. | |||
| if that declaration is not used. The parameter needs to be local | |||
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nit: needs to be local -> needs to be a local
p4-16/spec/P4-16-spec.mdk
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| The type `string` represents strings. There are no operations on | ||
| string values; one cannot declare variables with a `string` type. | ||
| Parameters with type `string` can be only directionless (see Section | ||
| The type `string` represents strings. The values are either string |
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It's a bit strange to think of concatenations as being values... Maybe "string-typed expressions are either string literals or concatenations of multiple string-typed expressions."?
| @@ -1304,8 1304,8 @@ number of backslash characters (ASCII code 92). P4 does not make any | |||
| validity checks on strings (i.e., it does not check that strings | |||
| represent legal UTF-8 encodings). | |||
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| Since P4 does not provide any operations on strings, | |||
| string literals are generally passed unchanged through the P4 compiler to | |||
| Since P4 does not allow strings to exist at runtime, string literals | |||
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I think this isn't really true anymore? Now we also concatenate them e.g.? And I'm guessing we plan to turn that into a single string literal before passing it along to backends (though maybe not?).
I think the point of this paragraph is to say that the P4 compiler won't interpret string literals. What does that mean in the new world with concatenation?
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Probably terminating quotes are no longer left as-is?
p4-16/spec/P4-16-spec.mdk
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| The only operation allowed on strings is concatenation, denoted by | ||
| ` `. For string concatenation, both operands must be strings and | ||
| the result is also a string. String concatenation can be only |
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nit: can only be* performed
p4-16/spec/P4-16-spec.mdk
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| body. In the | ||
| following example, the fully-qualified name of the table is `c_inst.t1`. | ||
| language element from the control plane. This annotation takes a local | ||
| compile-time know value of type `string` (typically a string literal). |
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nit: know -> known*
p4-16/spec/P4-16-spec.mdk
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| deprecated construct. This is mostly useful for annotating library | ||
| constructs, such as externs. | ||
| deprecated construct. This is mostly useful for annotating library | ||
| constructs, such as externs. The parameter needs to be local |
There was a problem hiding this comment.
Would also go with 'must be' over 'needs to be' imo.
Signed-off-by: Vladimir Still <[email protected]>
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Thanks for the comments and sorry for the delayed response. I think I've fixed all the issues now. |
This gives wording to #1297, the compile-time concatenation of strings. The P4C part of this is p4lang/p4c#4856. The changes are relatively small, I hope I have not missed any more parts that mention that there are no string operations. Note that as stated here, it also allows string concatenation in
@name,@deprecatedand@noWarnpragmas. The last one has probably no use for it, but I think it is better to be consistent there.Resolves #1297.