Essential Macros Code Examples
Copyright 2014 Dave Gurnell of Underscore http://underscore.io
Licensed under the Apache License v2.0 http://www.apache.org/licenses/LICENSE-2.0.html
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Each example is split into two projects,
lib defines the macros and
app makes use of them.
hello - Hello world written as a macro. The macro embeds a compilation timestamp in the printed message to demonstrate that it is executed at compile time. This is contrasted with regular code that prints a timestamp at run time.
maximum - Simple project demonstrating basic setup. The macro itself,
maximum, isn't particularly useful, but the project serves as a good example of the various concepts in play.
printtree - Macro that uses
showRawto print the desugared syntax and underlying tree structure of arbitrary snippets of Scala code. Good for doing research in advance of writing new macros.
simpleassert - Macro demonstrating simple pattern matching on trees using quasiquotes. Slightly improved version of Scala's built-in
assertmethod that prints various values involved in the assertion.
betterassert - Macro demonstrating more advanced tree inspection using pattern matching and tree traversal. Improved version of
simpleassertthat prints useful debugging information in a much wider range of cases.
printtype - Family of generic macros that print a variety of information about their type parameters.
orderings - Code generation macro that inspects a type and creates an object allowing sorting by any of its fields. This technique is useful when writing, for example, a web service that allows users to sort a database by any field in the returned data.
enumerations - Generating the set of instances of a sealed trait. Useful for rolling your own enumerations via sealed case objects.
whitebox - Simple project demonstrating the fundamental difference between whitebox and blackbox macros. See comments in the main application file for details.
validation - Sketch of a codebase for a validation library that automatically tags errors using the names of the erroneous fields. One significant property is that the macro is implemented as a chainable method call rather than as a top-level function.
csv - Sketch of a type-class-based codebase for CSV serialization. An implicit macro is used to support automatic materialization of type class instances for case classes.