Why does Magento 2 composer.json require composer?

Question

Perhaps a stupid question but: Why does Magento 2 composer.json require Composer?

If you look at the composer.json (either of the GitHub repo or the composer.json bundled with the downloaded archive from magento.com), you'll see something like:

"require": {
  ...
  "composer/composer": "@alpha"
  ...
}

or:

"require": {
  ...
  "composer/composer": "1.4.1"
  ...
}

So my question basically is: Why would Magento (or any given Composer project) require composer itself? I mean: You typically should already have installed composer on your system as a global library. So why include it then?

Answer 1

Most likely because the Magento composer installer which is part of the Magento composer meta package needs a specific version and this way it has access to the code.