Sequence Diagram: Original

• Scenario: Single key/value
•        Docker Report code
•        Low-level YAML parsing code
•        YAML parsing loop code
• Full Diagram

UML Class Diagram: Current YAMLParser

• The multiple public methods correspond to specific predicates and parsing
• Requires complex use by the client (DockerReport)
• Low-level parsing is encapsulated and follows information hiding
• High-level code for parsing is still in the application

Sequence Diagram: YAMLParser

• Scenario: Single key/value
•        Docker Report
•        Low-level YAML parsing
•        YAML parsing loop
• Many YAML concerns still exist in DockerReport
• Cannot move loop concern to YAMLParser because of repeated calls to code with DockerReport concerns
• Full Diagram
• Compare to Original

Inversion of Control (IoC)

• Inverts part of the control flow of the program
• Instead of your code calling a function/method, you register parts of your code, and the function/method calls those parts of your code at the appropriate time
• Similar to much event-driven programming
• For low-level functionality with a function, typically called a callback
• May be a single method or an entire object
• Essential for frameworks

Extension Points

• What points in the program can you register a handler for
• Every extension point has a single handler
• The handler is passed all data as parameters
• In all our examples, the parameters are IN, but with some IoC, the parameters can be OUT or IN/OUT

YAMLParser Extension Points

• Start Document
• Key: name
• Value: value
• End Document

UML Class Diagram: YAMLParser IoC

• Single public method, parse() is the only one the client uses to parse the YAML
• All predicates and parsing methods are now private
• Straightforward use by the client (DockerReport)
• Low-level parsing is encapsulated and follows information hiding
• High-level code for parsing is in the parse() method

IoC YAMLParser

• Scenario: Single key/value
•        Docker Report
•        Low-level YAML parsing
•        YAML parsing loop
• Full Diagram
• Compare to non-IoC

IoC YAMLParser: Registration

Adding Handlers