Create 2015-6-18-repeated-byname

odersky · odersky · commit ad9514d4e99a · 2015-06-18T16:32:31.000+02:00
diff --git a/sips/pending/_posts/2015-6-18-repeated-byname b/sips/pending/_posts/2015-6-18-repeated-byname
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+## Motivation
+
+Scala so far does not allow by-name repeated parameters. But I can't see a good reason why this combination should be disallowed. Also, the combination is necessary to allow vararg parameters that are passed as expressions to inline methods (instead of being lifted out).
+
+## Syntax
+
+The syntax for `ParamType` becomes
+
+      ParamType         ::=  [`=>'] ParamValueType
+      ParamValueType    ::=  Type [`*']              
+
+The syntax implies that a type such as `=> T*`, which is both by-name and repeated is interpreted as `=> (T*)`, that is, as a by-name type of a repeated type.
+
+## Translation Rules
+
+If a parameter has a by-name repeated type `=> T*` it matches an arbitrary number of actual arguments of type `T`. As usual for by-name parameters, the arguments are not evaluated at the point of call. Instead, all arguments are evaluated each time the parameter is referenced in the called method.
+
+The same holds for an vararg argument of the form `e: _*`. The argument expression `e` is evaluated each time the parameter is referenced in the called method.
+
+## See also
+
+https://github.com/lampepfl/dotty/issues/499
