Question

I have an object that is responsible for exporting a file to csv.

It works well but i am looking at ways to refactor it.

This question pertains to the constructor which takes a number of arguments, relating to how the csv is to be exported:

For example, file name, delimiter, etc. etc.

Also, lately I have been reading about dependency injection but cant decide if this is a case where I should:

A. Leave the constructor as is.
B. Create a new class that gets passed to the constructor that simple holds config values for the file name etc
C. Something else altogether?

Here is the existing constructor (in PHP)

    public function __construct($file,$overwriteExistingFile, $enclosure, $delim, $headerRow)
    {
        //set all properties here
    }

Answer 1

Each of those values represents data that is an input to some process. $enclosure, $delimiter, and $headerRow pertain to generating the CSV content, while $file and $overwriteExistingFile pertain to persisting the content to disk.

A hallmark of a DI-style refactoring is to identify the various responsibilities (generate, persist) and encapsulate each of them in its own type. This shifts the refactoring from “how do I best get the values to this class?” to “how do I remove knowledge of these values from this class?”

To answer that, we would define two new concepts, each of which takes one of the responsibilities, and pass those into the existing constructor:

public function __construct($csvGenerator, $csvFileWriter)
{
    ...save dependencies...
}

...at some point, generate the CSV content and pass it to the file writer...

In this way, the original class becomes the orchestrator of the interaction between the generation and file writing, without having intimate knowledge of either activity. We have elevated the class to a higher level of abstraction, simplifying it as well as isolating its responsibilities into its collaborators.

Now, you would define two new classes, constructing them with the relevant parameters:

Generator

public function __construct($enclosure, $delimiter, $headerRow)

File Writer

public function __construct($file, $overwriteExistingFile)

With these elements in place, you can compose them together by creating the generator, then the file writer, then passing both to the orchestrator.