Classes with one public function replaced with a constructor

Question

I have a number of classes with a single public method. Looking at this answer, I tend to agree with what is stated.

The OP lists some examples, which I interpret to be used like

(new VideoCompressor)->compress($raw_video);

While the readability improves slightly by calling the explicit method name, I feel it is almost as readable by simply moving the parameters to a __construct() and calling the compress function from within the constructor.

new VideoCompressor($raw_video);

This however would add a constructor to the class if it didn't have one already.

In my eyes it would be a trade between slightly smaller calls to classes in exchange for more code within the class.

Is there any other reason either method should be preferred other than personal taste?

What if the method isn't void? – Roman Reiner Oct 02 '15 at 15:45 — Roman Reiner, Oct 02 '15 at 15:45
You might as well just have a static function – whatsisname Oct 02 '15 at 17:39 — whatsisname, Oct 02 '15 at 17:39

score 5 · Accepted Answer · answered Oct 02 '15 at 14:27

5

Would this work? Yes. Is this proper class design? No.

A constructor's purpose is to ensure valid creation (construction) of the instance, no more and no less.

answered Oct 02 '15 at 14:27

Phil Sandler

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score 3 · Answer 2 · edited Apr 12 '17 at 07:31

3

Calling the compress function is the correct approach. That way you can easily implement multiple compression methods.

interface VideoCompression
{
    public function compress($rawVideo);
}

final class MP4VideoCompression implements VideoCompression
{
    public function compress($rawVideo) { }
}

final class H264VideoCompression implements VideoCompression
{
    public function compress($rawVideo) { }
}

Then later in your app you can get the video compression class based on user's input via a factory, for example.

Update: After checking the original thread I realized MainMa posted exactly the same approach as me with further reasons why to use that way.

edited Apr 12 '17 at 07:31

Community

1

answered Oct 02 '15 at 14:25

Andy

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4
25
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Technically though, couldn't you do the exact same but using a constructor for each? – myol Oct 02 '15 at 14:31
@myol It would, but how would you name your class then? A `H264VideoCompressionWhichCompressesVideoOnConstruct` looks really bad. – Andy Oct 02 '15 at 14:42
ok fair point :) – myol Oct 02 '15 at 14:49

score 1 · Answer 3 · answered Oct 02 '15 at 14:32

As a quick example. I hope you see that tieing the consturction of an object to the moment of use eliminates dependancy injection, ties you to a concrete type eliminating polymorphism (using a different IVideoCompressor is now impossible) and is generally bad:

    interface IVideoCompressor
    {
        Compress();
    }

    class VideoCompressor : IVideoCompressor
    {
        public byte[] Compress(byte[] input){
             throw new NotImplementedException();
        }
    }

    public class DirectoryFiddler
    {
        IVideoCompressor _videoComp;

        public DirectoryFiddler(IVideoCompressor videoComp, IImageCompressor imageCOmp)
        {
            _videoComp = videoComp;
        }

        public byte[] DoSomething(Idirectory directory)
        {
            // DI, polymorphism, in general good stuff
            return _videoComp.Compress(directory.Video);
        }

        public byte[] DoSomething2(Idirectory directory)
        {
            // Tied to VideoCompressor
            return new VideoCompressor(directory.Video).Compress();
        }
    }

Classes with one public function replaced with a constructor

3 Answers3