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VM should support new optional parameters syntax #4290
The plan is the following:
"Optional elements of production" have nothing to do with optional parameters. They refer to the metasyntax (i.e. notation in the spec itself) used to specify Dart syntax.
The ?v notation refers to the argument definition test (feature request issue #4265). Here is the relevant section:
An argument definition test is an expression that tests whether a formal parameter is bound to an object explicitly passed to a method or function.
An argument definition test e of the form ?v evaluates to true iff the currently executing invocation of the function that declares v explicitly provided an argument for the formal parameter v; otherwise e evaluates to false.
It is a compile time error if v does not denote a formal parameter. The static type of an argument definition test is bool.