Working with the context

Each machine allows you to mutate a value when events happen. For example, you can count how many times a state has been reached.

Defining the context type

The context datatype is defined as the third generic type of the machine. In the following example we will use an int value:

string initialState = "...";

var machineBlueprint = StateMachine<string, string, int>.Factory((builder) =>
{
    /* ... */
}, initialState);

You can define the initial context value by providing another argument after the initialState.

string initialState = "...";
int initialContext = 0;

var machineBlueprint = StateMachine<string, string, int>.Factory((builder) =>
{
    /* ... */
}, initialState, initialContext);

Mutating the context

You might want to mutate the context value when some events happen. You can do so by using the SetContext and MutateContext methods.

• SetContext: accepts a context value. It updates the context setting it to whatever value you passed as an argument.
• MutateContext: accepts a function. The function provides as a parameter the current context value and updates the context with the return value.

Lets see how:

string initialState = "day";
int initialContext = 0;
string ACTION = "next";

var machine = StateMachine<string, string, int>.Factory((builder) =>
{
    /* Define day state & transition to night */
    var dayState = builder.AddState("day");
    dayState.AddTransition(ACTION, "night");

    /* Define night state & transition to day */
    var nightState = builder.AddState("night");
    nightState.AddTransition(ACTION, "day");

    /* We add an event that increments the context by one when we enter the day state */
    dayState.OnEnter((info) => {
        var machine = info.Machine;
        machine.MutateContext((context) => context + 1);
    });
}, initialState, initialContext);

This example shows us a state machine that switchs between day and night and counts how many days have passed.