If Ruby converts such arguments into a hash, both of those attributes would be lost.

Definitely, and this is why RubyCocoa wasn’t able to use this syntax for Objective-C selector messaging. In 1.9, hash keys are ordered in the same way they are provided, but this still doesn’t solve the multiple keys problem. MacRuby has a modified copy of the Ruby parser that is now able to reconstruct the complete selector (internally it doesn’t use a Hash anymore but a list of key/pair elements. It still sends a Hash if the receiver doesn’t respond to the selector, to preserve compatibility.

We can’t re-implement the entire Ruby semantics with the Objective-C runtime. For example, it doesn’t support instance variables to be added at runtime into a class, or classes to be nested. So, Ruby classes in MacRuby are not 100% Objective-C classes, because we still allocate some extra data structure to store the Ruby bits. But, Ruby objects are Objective-C objects, and Ruby methods are available in the Objective-C runtime.

Regarding the marshaling overhead, a MacRuby message will be of course slower than sending the same message in straight Objective-C. But as Jens says, since we don’t have to convert the arguments and the return value, it’s much more faster than a bridging solution. I also plan to unify the Ruby exception model with the same one as Objective-C, which has a costless “try” operation on 64-bit.

Will it be fast? I think it should be fast enough :)

I’m sure metaclasses will be tricky. But the Obj-C runtime gives you a fair amount of control over method resolution, so I suspect it’ll be possible somehow. It sounds as though they want to do a faithful implementation of Ruby, not something just Ruby-like.

It’s a small point, but even using the Obj-C runtime completely in all other respects can’t eliminate marshalling overhead, unless you’re also generating machine code in the same way the gcc/clang compilers are doing, and then you’re not in the interpreted (Ruby VM) world any more.

I’m thinking about this, as I’m working on a similar project, and I don’t see any way around this (short of Obj-C-style code generation).

Another nice feature of MacRuby is that it slightly extends Ruby’s method-call syntax to allow Objective-C style interleaved keywords and arguments.

Actually, it does not. That syntax is already available in plain Ruby. The ‘alternative’ syntax is available in Ruby 1.8, while Ruby 1.9 supports the more Objective-C like syntax. Do this in plain-jane irb with Tiger or Leopard (hope this gets formatted properly):


?> def thing(one, two)
>> puts one
>> puts two.inspect
>> end
=> nil
>> thing('equation', 'hot' => 'cold', 'love' => 'hate')
equation
{"love"=>"hate", "hot"=>"cold"}
=> nil