Singleton (Groovy 2.4.7)
Date: 2016-06-03

groovy.lang

## Annotation Type Singleton

-     @Documented
      @Retention(value=SOURCE)
      @Target(value=TYPE)
      public @interface Singleton

  Class annotation to make a singleton class. The singleton is obtained through normal property access using the singleton property (defaults to "instance"). Such classes can be initialized during normal static initialization of the class or lazily (on first access). To make the singleton lazy use `@Singleton(lazy=true)`. Lazy singletons are implemented with double-checked locking and a volatile backing field. By default, no explicit constructors are allowed. To create one or more explicit constructors use `@Singleton(strict=false)`. This could be used to:
  - provide your own custom initialization logic in your own no-arg constructor - you will be responsible for the entire code (the `@Singleton` annotation becomes merely documentation)
  - provide one or more constructors with arguments for a quasi-singleton - these constructors will be used to create instances that are independent of the singleton instance returned by the singleton property
  Author:
    Alex Tkachman, Paul King

- - ### Optional Element Summary

    Optional Elements
    Modifier and Type | Optional Element and Description
    --- | ---
    `boolean` | `lazy`
    `String` | `property`
    `boolean` | `strict`

- - ### Element Detail

    - #### lazy

          public abstract boolean lazy

      Returns:
        if this singleton should be lazy
      Default:
        false

    - #### strict

          public abstract boolean strict

      Returns:
        if this singleton should have strict semantics
      Default:
        true

    - #### property

          public abstract String property

      Returns:
        the singleton property name
      Default:
        "instance"