> I am talking about what value you could pass into the multiple dispatch code in the article I linked to
Ah, I misunderstood the question. Yes, in that case it's fairly type-safe.
> The actual reflection going on in the code I posted for multiple dispatch would surely be nothing more than an int comparison
Is this based on gut reaction or are you talking about optimizations that `dynamic` performs? I ask because my understanding is that `dynamic` is like a really efficient reflection-emitter, that attempts to do at runtime the same thing that the compiler would do at compile time, but slower because it has to look stuff up via reflection.
From Eric Lippert [2]:
> The magic is: the compiler emits code that starts the C# compiler again at runtime. The runtime version of the compiler analyzes the call as though the compile-time types of all the objects had been their actual runtime types, generates an expression tree representing that call, compiles the expression tree, caches the delegate for next time, and runs the delegate.
So maybe `dynamic` at runtime figures out that it can do a "a struct with an int tag to represent the type, and a void pointer for its value", but I wouldn't assume it does and from what I've read on it, I wouldn't think that it does.
Base classes already have to carry their runtime type with them anyway. As do nodes of an algebraic data type. You may well be right that the compiler might not be "sufficiently smart" to see this very limited use of dynamic and realise no special reflection magic is actually required. But considering dynamic is only used to actually pull out the runtime type in the example code, and not to call arbitrary methods on it that may or not be there, I assumed - maybe wrongly - that the runtime hit would be the same as the branching that occurs in Ocaml or Haskell or F# when it comes across a "match" statement.
But to answer your question - yes, entirely based on gut reaction and what a compiler would ideally be able to do given the code posted. So very probably wrong.
Ah, I misunderstood the question. Yes, in that case it's fairly type-safe.
> The actual reflection going on in the code I posted for multiple dispatch would surely be nothing more than an int comparison
Is this based on gut reaction or are you talking about optimizations that `dynamic` performs? I ask because my understanding is that `dynamic` is like a really efficient reflection-emitter, that attempts to do at runtime the same thing that the compiler would do at compile time, but slower because it has to look stuff up via reflection.
From Eric Lippert [2]:
> The magic is: the compiler emits code that starts the C# compiler again at runtime. The runtime version of the compiler analyzes the call as though the compile-time types of all the objects had been their actual runtime types, generates an expression tree representing that call, compiles the expression tree, caches the delegate for next time, and runs the delegate.
[2]: http://stackoverflow.com/questions/10330805/c-sharp-multiple...
So maybe `dynamic` at runtime figures out that it can do a "a struct with an int tag to represent the type, and a void pointer for its value", but I wouldn't assume it does and from what I've read on it, I wouldn't think that it does.