MacMemo

MacMemo is a simple library introducing @memoize macro annotation for simple function memoization. Annotated functions are wrapped with boilerplate code which uses Guava CacheBuilder (or any other cache implementation - see 'Custom memo cache builders' section) to save returned values for given argument list. Memoization is scoped for particular class instance.

Available for Scala 2.11 and 2.12

Example usage:

import com.softwaremill.macmemo.memoize

class GraphBuilder {

  @memoize(maxSize = 20000, expiresAfter = 2 hours)
  def creatGraph(elementCount: Int): Graph = {
    someExpensiveCode()
  }

}

Parameters (for more details see Guava docs):

• maxSize: Specifies the maximum number of entries the cache may contain.
• expiresAfter: Specifies that each entry should be automatically removed from the cache once a fixed duration has elapsed after the entry's creation, or the most recent replacement of its value.
• concurrencyLevel: Guides the allowed concurrency among update operations.

Installation, using with SBT

The jars are deployed to Sonatype's OSS repository. To use MacMemo in your project, add a dependency:

libraryDependencies += "com.softwaremill.macmemo" %% "macros" % "0.4"

You also need to add a special compiler plugin to your buildSettings:

addCompilerPlugin("org.scalamacros" % "paradise" % "2.1.0" cross CrossVersion.full)

Testability

In order to disable MacMemo for tests, add following test options to your buildSettings:

testOptions in Test += Tests.Setup(() => System.setProperty("macmemo.disable", "true"))

Debugging

The print debugging information on what MacMemo does when generating code, set the macmemo.debug system property. E.g. with SBT, just add a System.setProperty("macmemo.debug", "") line to your build file.

Custom memo cache builders

One may want to use more sophisticated cache provider, than simple Guava Cache. It's possible to leverage any of existing cache providers like memcached or even NoSQL databases like Redis, by bringing appropriate implicit com.softwaremill.macmemo.MemoCacheBuilder instance into memoized class scope (the scope of the method definition, not it's usage, e.g: companion object, implicit val within class or an explicit imports available in scope of class definition)

See MemoCacheBuilder.guavaMemoCacheBuilder in macmemo/macros/src/main/scala/com/softwaremill/macmemo/MemoCacheBuilder.scala, macros/src/test/scala/com/softwaremill/macmemo/TestMemoCacheBuilder.scala and
macros/src/test/scala/com/softwaremill/macmemo/examples/MemoCacheBuilderResolutionSpec.scala for custom builder implementation and usage examples.

Whenever custom memo builder cannot be found in class definition scope, appropriate compiler info message will be emitted:

[info] /path/to/sources/SomeFancyNamedFile.scala:42: Cannot find custom memo builder for method 'someMethodName' - default builder will be used
[info]   @memoize(maxSize = 2, 15 days)
[info]    ^

Currently there is no way to turn them off.

Credits

Special thanks to Adam Warski for his clever MacWire library and all other inspirations :)