F# – Duck Typing and Structural Typing

re: F# – Duck Typing and Structural Typing

podwysocki — Tue, 16 Jun 2009 00:02:01 GMT

@Michael,

Yes, that's another form of Structural typing. I guess this was a bit confusing and I should clear that up.

Matt

re: F# – Duck Typing and Structural Typing

Kurt Schelfthout — Sun, 14 Jun 2009 08:17:38 GMT

...the "Convert Damnit" operator...

Heh. Good one. :)

re: F# – Duck Typing and Structural Typing

Michael Giagnocavo — Sat, 13 Jun 2009 02:22:53 GMT

@thelazydogsback -- The CLR doesn't support it directly (member constraints on generics), so C# doesn't either. It's only because the F# compiler has inlining and statically-resolved type parameters that we can do cool stuff like this.

re: F# – Duck Typing and Structural Typing

Michael Giagnocavo — Sat, 13 Jun 2009 01:30:01 GMT

I thought structural typing was in contrast to nominative typing. If F# had structural typing, this would work:

> type Foo = {x:int}

type Bar = {x:int}

let a : Foo = { x = 1 }

let b : Bar = { x = 1 }

a = b;;

----^

stdin(5,5): error FS0001: This expression has type

Bar

but is here used with type

Foo

re: F# – Duck Typing and Structural Typing

thelazydogsback — Fri, 12 Jun 2009 17:08:12 GMT

> only known at compile-time

-->

only known at run-time

re: F# – Duck Typing and Structural Typing

thelazydogsback — Fri, 12 Jun 2009 00:27:20 GMT

let inline getName arg =

( ^a : (member Name : string) arg)

Pretty powerful - a nice blend of flexibility and compile-time safety.

Am I correct in that the above code is not expressable in C# without code gen or reflection? (Ignoring that the implicit op would work in the case anyway.)

Can the name be a quotation hole in case the name is only known at compile-time and we want to pregenerate the getter rather than use reflection each time?