|
Scala example source code file (Context.scala)
The Context.scala Scala example source codepackage scala package reflect package macros package blackbox /** * <span class="badge badge-red" style="float: right;">EXPERIMENTAL</span> * * The blackbox Scala macros context. * * See [[scala.reflect.macros.package 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 `blackbox.Context`, then this macro def becomes a blackbox macro, * which means that its expansion will be upcast to its return type, enforcing faithfullness of that macro to its * type signature. Whitebox macros, i.e. the ones defined with `whitebox.Context`, aren't bound by this restriction, * which enables a number of important use cases, but they are also going to enjoy less support than blackbox macros, * so choose wisely. See the [[http://docs.scala-lang.org/overviews/macros.html Macros Guide]] for more information. * * @see `scala.reflect.macros.whitebox.Context` */ trait Context extends Aliases with Enclosures with Names with Reifiers with FrontEnds with Infrastructure with Typers with Parsers with Evals with ExprUtils with Internals { /** The compile-time universe. */ val universe: Universe /** The mirror of the compile-time universe. */ val mirror: universe.Mirror /** The type of the prefix tree from which the macro is selected. * See the documentation entry for `prefix` for an example. */ type PrefixType /** The prefix tree from which the macro is selected. * * For example, for a macro `filter` defined as an instance method on a collection `Coll`, * `prefix` represents an equivalent of `this` for normal instance methods: * * {{{ * scala> class Coll[T] { * | def filter(p: T => Boolean): Coll[T] = macro M.filter[T] * | }; object M { * | def filter[T](c: Context { type PrefixType = Coll[T] }) * | (p: c.Expr[T => Boolean]): c.Expr[Coll[T]] = * | { * | println(c.prefix.tree) * | c.prefix * | } * | } * defined class Coll * defined module Macros * * scala> new Coll[Int]().filter(_ % 2 == 0) * new Coll[Int]() * res0: Coll[Int] = ... * * scala> val x = new Coll[String]() * x: Coll[String] = ... * * scala> x.filter(_ != "") * \$line11.\$read.\$iw.\$iw.\$iw.\$iw.\$iw.\$iw.\$iw.\$iw.\$iw.\$iw.\$iw.\$iw.x * res1 @ 35563b4b: x.type = ... * }}} * * Note how the value of `prefix` changes depending on the qualifier of the macro call * (i.e. the expression that is at the left-hand side of the dot). * * Another noteworthy thing about the snippet above is the `Context { type PrefixType = Coll[T] }` * type that is used to stress that the macro implementation works with prefixes of type `Coll[T]`. */ val prefix: Expr[PrefixType] } Other Scala source code examplesHere is a short list of links related to this Scala Context.scala source code file: |
... this post is sponsored by my books ... | |
#1 New Release! |
FP Best Seller |
Copyright 1998-2024 Alvin Alexander, alvinalexander.com
All Rights Reserved.
A percentage of advertising revenue from
pages under the /java/jwarehouse
URI on this website is
paid back to open source projects.