Readme.md

Mutable State: Global vs Local

Note: This file will use the function, traceM. This function will be explained in the Hello World/Debugging folder. Please read through that entire folder before continuing here.

There are two types of mutable state:

	Global	Local
Creatable in...	Anywhere	Local scope
Readable from...	Anywhere that has its reference	Local Scope
Writable to...	Anywhere that has its reference	Local Scope
Destroyed when...	Program Exits?	Exit Local Scope

Using Java as an example...

public class StateExample {
  // note the absence of "final"
  public String GLOBAL_STATE = "some state";

  public static int function() {
    String localState = "some value";
    localState = localState + "some other string";
    return localState.length();
  }

  public static void example1() {
    // change global state
    GLOBAL_STATE = "first change!";
    // localState changed, but we can't change
    //   it outside of it's scope
    function();
  }

  public static void example2() {
    // change global state again
    GLOBAL_STATE = "second change!";
  }
}