Hands-On Design Patterns and Best Practices with Julia

Introducing the file logger use case

Let's consider a use case for building a file logging facility. 

Suppose that we want to provide an API for logging messages to files based upon a set of logging levels. By default, we will support three levels: info, warning, and error. A logger facility is provided so that a message will be directed to a file, as long as it comes with a high enough logging level.

The functional requirements can be summarized as follows:

• An info-level logger accepts messages with info, warning, or error levels.
• A warning-level logger accepts messages with warning or error levels only.
• An error-level logger accepts messages with an error level only.

To implement the file logger, we will first define some constants for ...