> On Nov 20, 2017, at 12:32 AM, David Waite via swift-evolution > <swift-evolution@swift.org> wrote: > >> On Nov 20, 2017, at 1:16 AM, David Hart via swift-evolution >> <swift-evolution@swift.org <mailto:swift-evolution@swift.org>> wrote: >> > <snip> > >> Moreover, Ruby allows classes to have instance variables with the same name >> as methods: >> >> class Foo >> def initialize() >> @bar = 5 >> end >> >> def bar() >> puts “Hello" >> end >> end >> >> In that case, how would one implement DynamicMemberLookupProtocol for the >> lookup of bar, and what would the return value be? Its entirely context >> sensitive. > > I do not believe Ruby does not give you direct external access to variables. > Everything with a ‘.’ is a function call. > > You would use e.g. > > Foo.new.instance_variable_get("@bar”) // => 5 > > attr :bar exposes a variable @bar through functions bar() and bar=() (and > also optimizes storage in some implementations)
This is correct…sort of. Ruby uses symbols to refer to both methods and instance variables, but instance variable symbols always start with @, so they effectively belong to a different namespace. (Similarly, symbols starting with a capital letter are for constants; symbols starting with @@ are for class variables; I believe symbols starting with $ are for global variables.) Ruby only provides syntax to access another object's methods and (for a class) constants, so in practice there's no way to access another object's instance variables except by calling a method on it, but there's no particular reason our bridge would need to follow that rule. Leaving aside those technicalities, it's pretty clear that `foo.bar` should access a method, not an instance variable, when `foo` is a Ruby object. That doesn't mean it's the same as Python, though, because in Ruby it will need to *call* the method immediately if we're to provide natural syntax for Ruby objects bridged to Swift. Bottom line: Ruby cannot be bridged naturally with just an undifferentiated "access member" hook. It needs separate "access property" and "access method" hooks. -- Brent Royal-Gordon Architechies
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