Package scala.reflect.macros.whitebox

EXPERIMENTAL

The whitebox Scala macros context.

See the overview page for a description of how macros work. This documentation entry provides information on the API available to macro writers.

A macro context wraps a compiler universe exposed in universe and having type scala.reflect.macros.Universe. This type is a refinement over the generic reflection API provided in scala.reflect.api.Universe. The extended Universe provides mutability for reflection artifacts (e.g. macros can change types of compiler trees, add annotation to symbols representing definitions, etc) and exposes some internal compiler functionality such as Symbol.deSkolemize or Tree.attachments.

Another fundamental part of a macro context is macroApplication, which provides access to the tree undergoing macro expansion. Parts of this tree can be found in arguments of the corresponding macro implementations and in prefix, but macroApplication gives the full picture.

Other than that, macro contexts provide facilities for typechecking, exploring the compiler's symbol table and enclosing trees and compilation units, evaluating trees, logging warnings/errors and much more. Refer to the documentation of top-level traits in this package to learn the details.

If a macro def refers to a macro impl that uses whitebox.Context, then this macro def becomes a whitebox macro, gaining the ability to refine the type of its expansion beyond its official return type, which enables a number of important use cases. Blackbox macros, i.e. the ones defined with blackbox.Context, can't do that, so they are less powerful. However blackbox macros are also going to enjoy better support than whitebox macros, so choose wisely. See the Macros Guide for more information.