https://github.com/state-machine-systems/dynamic-reference

Dynamically-scoped variables for Java
https://github.com/state-machine-systems/dynamic-reference

Last synced: 6 months ago
JSON representation

Dynamically-scoped variables for Java

• Host: GitHub
• URL: https://github.com/state-machine-systems/dynamic-reference
• Owner: state-machine-systems
• License: apache-2.0
• Created: 2015-04-28T15:21:57.000Z (about 11 years ago)
• Default Branch: master
• Last Pushed: 2015-08-28T08:32:31.000Z (almost 11 years ago)
• Last Synced: 2025-07-13T02:43:04.649Z (12 months ago)
• Language: Java
• Size: 160 KB
• Stars: 0
• Watchers: 1
• Forks: 0
• Open Issues: 0
• Metadata Files:
  • Readme: README.md
  • License: LICENSE.txt

Awesome Lists containing this project

README

          
Dynamically-scoped references offer a more disciplined alternative to global variables. They're a handy feature from

the Lisp family of languages.

In Java, `static` fields are equivalent to global variables, with all the bad stuff that entails. By contrast, you

create a `DynamicReference` with an initial default value, which can be overridden inside a given block

scope. Code inside the block (at any call depth) will automatically use the overridden value. After the block

finishes, the value reverts back.

Here's an example of overriding a reference to `System.out`:

    import com.statemachinesystems.util.DynamicReference;

    import java.io.*;

    ...

    DynamicReference out = new DynamicReference<>(System.out);

    PrintStream log = new PrintStream(new File("out.log"), "UTF-8");

    void sayHello() {

        out.get().println("Hello World!");

    }

    ...

    // write to standard output

    sayHello();

    ...

    out.withValue(log, () -> {

        // write to the log file

        sayHello();

    });

This implementation is based on the `DynamicVariable` class from the Scala standard library.

### Getting started

This library is in the Maven Central repo, so just add the following chunk to your pom.xml (or the equivalent for Gradle/SBT/whatever):

    

        com.statemachinesystems

        dynamic-reference

        1.0

    

© 2015 State Machine Systems Ltd. [Apache Licence, Version 2.0](http://www.apache.org/licenses/LICENSE-2.0)