Improve rules for nameonly/positional/nameless and required/optional … #3864
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| // * required: a caller has to supply an argument | ||
| // * optional: the parameter has a default value that is used if a caller omits passing a specific argument | ||
| // | ||
| // The syntax for giving a positional-only (i.e., nameless) parameter does not a default-value expression, so |
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does not a => does not allow a
| // | ||
| // At a call site, positional arguments are not allowed to follow named arguments. Therefore, if "x" is | ||
| // a nameonly parameter, then there is no way to supply the parameters after "x" by position. Thus, any | ||
| // parameter that follows "x" must either by passed by name or have a default value. That is, if a later |
| // "formal" is preceded by a nameonly parameter, but itself is neither nameonly nor has a default value | ||
| reporter.Error(MessageSource.Resolver, formal.tok, | ||
| $"this parameter is effectively nameonly (because of the earlier nameonly parameter '{nameOfMostRecentNameonlyParameter}'); " + | ||
| "declare it as nameonly or give it an default-value expression"); |
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a default-value expression
| @@ -275,15 +275,15 @@ module NameOnlyParameters { | |||
| least predicate LP(a: int, nameonly b: int, c: int := 100) | |||
| static greatest predicate GP(a: int, nameonly b: int := 75, c: int := 100) | |||
| } | |||
| iterator Iter(nameonly u: int, x: int) | |||
| iterator Iter(nameonly u: int, x: int) // error (x2, because of the desugaring of iterators): x is effectively nameonly, but not declared as such | |||
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Maybe we should come up with a testing file format where you can specify the expected error messages inline : )
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I do like being able to read the expected outcome in the test file itself. Therefore, I always put such "error" comments in the tests. But these comments aren't the exact error messages, don't capture column information, and in some cases are even placed only on a nearby line. It's plausible that we could turn these into a formally recognized testing file format.
keyboardDrummer
previously approved these changes
Apr 13, 2023
|
Such a nice quality of life improvement, thanks ! |
RustanLeino
dismissed stale reviews from keyboardDrummer and seebees
via
75b30b1
keyboardDrummer
approved these changes
Apr 24, 2023
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Fixes #3859
This PR allows more parameter declarations (for example, as suggested in #3859, a
nameonlyparameter with a default value can now be follow by othernameonlyparameters), clarifies some error messages, and gives new errors for useless situations (for example, a parameter's default value can not be used if it is followed by a positional-only parameter).The new rules
Formal parameters have three ways to indicate how they are to be passed in:
nameonly: the only way to give a specific argument value is to name the parameterA parameter is either required or optional:
The syntax for giving a positional-only (i.e., nameless) parameter does not a default-value expression, so a positional-only parameter is always required.
At a call site, positional arguments are not allowed to follow named arguments. Therefore, if
xis a nameonly parameter, then there is no way to supply the parameters afterxby position. Thus, any parameter that followsxmust either by passed by name or have a default value. That is, if a later parameter does not have a default value, it is effectively nameonly. We impose the rule thatFor a positional-only parameter
x, every parameter precedingxis effectively required. We impose the rule thatBy submitting this pull request, I confirm that my contribution is made under the terms of the MIT license.