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Libraries

This chapter will tell you how to make your library installable through Composer.

Every project is a package

As soon as you have a composer.json in a directory, that directory is a package. When you add a require to a project, you are making a package that depends on other packages. The only difference between your project and libraries is that your project is a package without a name.

In order to make that package installable you need to give it a name. You do this by adding a name to composer.json:

{
    "name": "acme/hello-world",
    "require": {
        "monolog/monolog": "1.0.*"
    }
}

In this case the project name is acme/hello-world, where acme is the vendor name. Supplying a vendor name is mandatory.

Note: If you don't know what to use as a vendor name, your GitHub username is usually a good bet. While package names are case insensitive, the convention is all lowercase and dashes for word separation.

Platform packages

Composer has platform packages, which are virtual packages for things that are installed on the system but are not actually installable by Composer. This includes PHP itself, PHP extensions and some system libraries.

php represents the PHP version of the user, allowing you to apply constraints, e.g. >=5.4.0. To require a 64bit version of php, you can require the php-64bit package.
ext-<name> allows you to require PHP extensions (includes core extensions). Versioning can be quite inconsistent here, so it's often a good idea to just set the constraint to *. An example of an extension package name is ext-gd.
lib-<name> allows constraints to be made on versions of libraries used by PHP. The following are available: curl, iconv, libxml, openssl, pcre, uuid, xsl.

You can use composer show --platform to get a list of your locally available platform packages.

Specifying the version

You need to specify the package's version some way. When you publish your package on Packagist, it is able to infer the version from the VCS (git, svn, hg) information, so in that case you do not have to specify it, and it is recommended not to. See tags and branches to see how version numbers are extracted from these.

If you are creating packages by hand and really have to specify it explicitly, you can just add a version field:

{
    "version": "1.0.0"
}

Note: You should avoid specifying the version field explicitly, because for tags the value must match the tag name.

Branches

For every branch, a package development version will be created. If the branch name looks like a version, the version will be {branchname}-dev. For example a branch 2.0 will get a version 2.0.x-dev (the .x is added for technical reasons, to make sure it is recognized as a branch, a 2.0.x branch would also be valid and be turned into 2.0.x-dev as well. If the branch does not look like a version, it will be dev-{branchname}. master results in a dev-master version.

Here are some examples of version branch names:

1.x
1.0 (equals 1.0.x)
1.1.x

Note: When you install a development version, it will be automatically pulled from its source. See the install command for more details.

Aliases

It is possible to alias branch names to versions. For example, you could alias dev-master to 1.0.x-dev, which would allow you to require 1.0.x-dev in all the packages.

See Aliases for more information.

Lock file

For your library you may commit the composer.lock file if you want to. This can help your team to always test against the same dependency versions. However, this lock file will not have any effect on other projects that depend on it. It only has an effect on the main project.

If you do not want to commit the lock file and you are using git, add it to the .gitignore.

Publishing to a VCS

Once you have a vcs repository (version control system, e.g. git) containing a composer.json file, your library is already composer-installable. In this example we will publish the acme/hello-world library on GitHub under github.com/username/hello-world.

Now, to test installing the acme/hello-world package, we create a new project locally. We will call it acme/blog. This blog will depend on acme/hello-world, which in turn depends on monolog/monolog. We can accomplish this by creating a new blog directory somewhere, containing a composer.json:

{
    "name": "acme/blog",
    "require": {
        "acme/hello-world": "dev-master"
    }
}

The name is not needed in this case, since we don't want to publish the blog as a library. It is added here to clarify which composer.json is being described.

Now we need to tell the blog app where to find the hello-world dependency. We do this by adding a package repository specification to the blog's composer.json:

{
    "name": "acme/blog",
    "repositories": [
        {
            "type": "vcs",
            "url": "https://github.com/username/hello-world"
        }
    ],
    "require": {
        "acme/hello-world": "dev-master"
    }
}

For more details on how package repositories work and what other types are available, see Repositories.

That's all. You can now install the dependencies by running Composer's install command!

Recap: Any git/svn/hg repository containing a composer.json can be added to your project by specifying the package repository and declaring the dependency in the require field.

Publishing to packagist

Alright, so now you can publish packages. But specifying the vcs repository every time is cumbersome. You don't want to force all your users to do that.

The other thing that you may have noticed is that we did not specify a package repository for monolog/monolog. How did that work? The answer is packagist.

Packagist is the main package repository for Composer, and it is enabled by default. Anything that is published on packagist is available automatically through Composer. Since monolog is on packagist, we can depend on it without having to specify any additional repositories.

If we wanted to share hello-world with the world, we would publish it on packagist as well. Doing so is really easy.

You simply hit the big "Submit Package" button and sign up. Then you submit the URL to your VCS repository, at which point packagist will start crawling it. Once it is done, your package will be available to anyone.

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