When to use Regexp.new()?

Question

I couldn't find any proper answer as Regexp stands for Regular Expressions. Here is an example: ``` test = Regexp.new("Hello") ``` It returns `/Hello/`, but I'm confused over the use of this. Why not use `/Hello/` directly? Can anyone give me a small example of `Regexp.new()` function?

Accepted Answer

Let's imagine you want to make your system detect "a sentence that starts with DOG and ends with CAT". Obvious Regex would be something like `/DOG.+CAT\./`[1].

So far, works. But now you'd like to be able to enhance the system, so the user can configure the opening and closing words. You might be able to do it with `//` syntax and interpolation:

```
/#{startWord}.+#{endWord}\./
```

but you also can do it with simple strings:

```
Regex.new(startWord + ".+" + endWord + "\.")
```

Cosmetics. Use what you like the most. However, there is one more thing that's important. With the `new` function, you can pass not only one, but also more parameters. See the docs.

So, the main[2] purpose of the existence of `new` from your point is actually being able to pass more arguments than just one. With `//` you can only pass the regex-formula[3]. With `new` you can pass options.

Few details were oversimplified for clarity. [1] It is not a valid "sentence detector". It is only some regex to show the problem. [2] It's not main purpose. The `new` is a constructor. It must exist or we would not be able to construct the object. Actually, the `/blargh/` syntax is translated into a `new` call. [3] Actually, with `//` you can pass some options too, like `/CaSEiNseNsiTive/i`. But, well, constructors are still more flexible.

When to use Regexp.new()?

Solution

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