A zero cost, type-safe equals function in scala
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import scala.language.experimental.macros | |
import scala.reflect.macros.Context | |
/** | |
* you can try this in the REPL even | |
*/ | |
object SafeEq { | |
/** | |
* eqv(1, "foo") won't compile | |
*/ | |
def eqv[A, B](a: A, b: B): Boolean = macro eqvMacro[A, B] | |
def eqvMacro[A, B](c: Context)( | |
a: c.Expr[A], | |
b: c.Expr[B])(implicit A: c.WeakTypeTag[A], B: c.WeakTypeTag[B]): c.Expr[Boolean] = { | |
import c.universe._ | |
if (A == B) c.Expr[Boolean](q"""$a == $b""") | |
else c.abort(c.enclosingPosition, s"types: $A and $B do not match") | |
} | |
} |
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Interesting. What's the advantage over the approach used by the === operator in spire? Here is the macro I use: https://github.com/non/spire/blob/master/macros/src/main/scala/spire/macros/Syntax.scala#L46
I think the performance characteristics should be the same, so I guess it is a matter of taste if you want the =:= in the type signature or not.