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Dependency injection for standalone Screenplay

If you are using Screenplay standalone then you are likely using the method Screenplay.ExecuteAsPerformanceAsync or one of its overloads.

Developers are urged to consider encapsulating their performance logic in a class which derives from IHostsPerformance. Through an overload (extension method) named ExecuteAsPerformanceAsync<T>, developers may specify the concrete implementation type of that class as a generic type parameter. This overload of ExecuteAsPerformanceAsync will resolve your class which derives from IHostsPerformance from dependency injection (remember to add it to the container!). This resolution will include all the class' dependencies which are constructor-injected and leads to very clean code. The service provider is never exposed, thus removing the temptation to use the service locator anti-pattern.

Example of the performance host technique

This example is functionally identical to the example below.

public class MyPerformance(ICast cast) : IHostsPerformance
{
    public Task<bool?> ExecutePerformanceAsync(CancellationToken cancellationToken)
    {
        var aaron = cast.GetActor<Aaron>();
        // Further performance logic ...
    }
}

// To consume the above:
await screenplay.ExecuteAsPerformanceAsync<MyPerformance>();

Alternative: Use a function

The original Screenplay.ExecuteAsPerformanceAsync overload accepts up to three parameters, the first of which is a function. That function should contain the logic which makes up the performance. The function (which drives the performance logic) provides two parameters itself:

The serivce provider may be used to resolve services which may be used by the performance logic.

Example of the function-based technique

This example is functionally identical to the example above.

await screenplay.ExecuteAsPerformanceAsync((services, cancellationToken) => {
    var cast = services.GetRequiredService<ICast>();
    var aaron = cast.GetActor<Aaron>();
    // Further performance logic ...
});
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