Attempting a by-name implicitly

nameplicitly.scala

import language.experimental.macros
import scala.reflect.makro.Context

object Name {

	def nameplicitly[T](implicit t0: T): Name[T] = macro nameplicitly_impl[T]

	def nameplicitly_impl[T : c.TypeTag](c: Context)(t0: c.Expr[T]): c.Expr[Name[T]] =
		c.reify(new Name[T] { def t = t0.splice })

}

trait Name[T] {
	def t: T
}

// now to test!

Welcome to Scala version 2.10.0-20120702-060901-33936243bd (OpenJDK 64-Bit Server VM, Java 1.7.0_05-icedtea).
Type in expressions to have them evaluated.
Type :help for more information.

scala> class Foo
defined class Foo

scala> implicit def foo = { println("o hai"); new Foo }
foo: Foo

scala> Name.nameplicitly[Foo]
res0: Name[Foo] = Name$$anon$1@54009218

scala> res0.t
o hai
res1: Foo = Foo@d64ea8b

scala> res0.t
o hai
res2: Foo = Foo@308f8cd8

Instead of c.Expr[T](t.tree) you can just write t.splice

Thanks, updated accordingly. Can you give me some pointers to further reading about what splice does exactly?

Hmm, the docs are scarce at the moment. Your best bet would be to read the macro SIP (but splice is called eval there :)).

…

On 3 July 2012 14:44, Lars Hupel < ***@***.*** > wrote: Thanks, updated accordingly. Can you give me some pointers to further reading about what `splice` does exactly? --- Reply to this email directly or view it on GitHub: https://gist.github.com/3039449

Oh, right, I was looking at that document and was confused about why eval didn't work as expected :) Thankfully, the error messages are very helpful.

What's the purpose (beside of learning macros)?

The initial problem came from @tonymorris, who had a problem with strict-only implicits (https://gist.github.com/3039030). After a quick discussion with @milessabin, I had the idea to try and implement it. It's basically a by-name implicitly.

If you declare nameplicitly as implicit, you also get an implicit Name[T] for any implicit T, like that:

def test(implicit byName: Name[Foo]) = byName.t

I should add that this essentially works around the problem that

def test(implicit byName: => Foo) = byName

does not work (rejected by compiler).

Ah, I see. Nice!