MacroAnnotation
Base trait for macro annotation that will transform a definition
Attributes
- Experimental
- true
- Graph
-
- Supertypes
Members list
Value members
Abstract methods
Transform the tree definition and add other definitions
Transform the tree definition and add other definitions
This method takes as argument the annotated definition. It returns a non-empty list containing the modified version of the annotated definition. The new tree for the definition must use the original symbol. New definitions can be added to the list before or after the transformed definitions, this order will be retained.
All definitions in the result must have the same owner. The owner can be recovered from tree.symbol.owner.
The result cannot contain class, object or type definition. This limitation will be relaxed in the future.
When developing and testing a macro annotation, you must enable -Xcheck-macros and -Ycheck:all.
Example:
import scala.quoted.*
import scala.collection.mutable
class memoize extends MacroAnnotation:
def transform(using Quotes)(tree: quotes.reflect.Definition): List[quotes.reflect.Definition] =
import quotes.reflect._
tree match
case DefDef(name, TermParamClause(param :: Nil) :: Nil, tpt, Some(rhsTree)) =>
(Ref(param.symbol).asExpr, rhsTree.asExpr) match
case ('{ $paramRefExpr: t }, '{ $rhsExpr: u }) =>
val cacheSymbol = Symbol.newUniqueVal(tree.symbol.owner, name + "Cache", TypeRepr.of[mutable.Map[t, u]], Flags.Private, Symbol.noSymbol)
val cacheRhs = '{ mutable.Map.empty[t, u] }.asTerm
val cacheVal = ValDef(cacheSymbol, Some(cacheRhs))
val cacheRefExpr = Ref(cacheSymbol).asExprOf[mutable.Map[t, u]]
val newRhs = '{ $cacheRefExpr.getOrElseUpdate($paramRefExpr, $rhsExpr) }.asTerm
val newTree = DefDef.copy(tree)(name, TermParamClause(param :: Nil) :: Nil, tpt, Some(newRhs))
List(cacheVal, newTree)
case _ =>
report.error("Annotation only supported on `def` with a single argument are supported")
List(tree)
with this macro annotation a user can write
@memoize
def fib(n: Int): Int =
println(s"compute fib of $n")
if n <= 1 then n else fib(n - 1) + fib(n - 2)
and the macro will modify the definition to create
val fibCache =
scala.collection.mutable.Map.empty[Int, Int]
def fib(n: Int): Int =
fibCache.getOrElseUpdate(
n,
{
println(s"compute fib of $n")
if n <= 1 then n else fib(n - 1) + fib(n - 2)
}
)
Value parameters
- Quotes
-
Implicit instance of Quotes used for tree reflection
- tree
-
Tree that will be transformed