A package that is not intended to be used as a library. Application packages may have dependencies on other packages, but are never depended on themselves. They are usually meant to be run directly, either on the command line or in a browser. The opposite of an application package is a library package.
Application packages should check their lockfiles into source
control, so that everyone working on the application and every location the
application is deployed has a consistent set of dependencies. Because their
dependencies are constrained by the lockfile, application packages usually
any for their dependencies’ version
else—intended to be part of a deployed package. The package can be a web
app, a package used by a web app, or any other package that benefits from a
build step. Tools such as
pub serve and
pub build take source assets (such as an HTML file, a CSS file, and
several Dart files) and produce generated assets (such as the same HTML and
Assets fall into four groups, with some overlap:
- Source asset: An actual, authored file on disk that
pub servecan find and use.
- Generated asset: An asset (possibly the output of a
transformer) that’s either served by
pub serveor saved to disk by
- Input asset: An asset that is the input to a transformer. An input asset might be a source asset, or it might be the output of a transformer in a previous phase.
- Output asset: An asset that is created by a transformer. An output asset might be a generated asset, or it might be the input to a transformer in a later phase.
Another package that your package relies on. If your package wants to import code from some other package, that package must be a dependency. Dependencies are specified in your package’s pubspec and described here.
“Entrypoint” is used to mean two things. In the general context of Dart, it is
a Dart library that is directly invoked by a Dart implementation. When you
reference a Dart library in a
<script> tag or pass it as a command line
argument to the standalone Dart VM, that library is the entrypoint. In other
words, it’s usually the
.dart file that contains
In the context of pub, an “entrypoint package” or “root package” is the root of a dependency graph. It will usually be an application. When you run your app, it’s the entrypoint package. Every other package it depends on will not be an entrypoint in that context.
A package can be an entrypoint in some contexts and not in others. Lets say your app uses a library package A. When you run your app, A is not the entrypoint package. However, if you go over to A and execute its unit tests, in that context, it is the entrypoint since your app isn’t involved.
A directory inside your package that is allowed to contain Dart entrypoints. Pub will ensure all of these directories get a “packages” directory, which is needed for “package:” imports to work.
Pub has a whitelist of these directories:
web. Any subdirectories of those (except
bin) may also
A package that other packages will depend on. Library packages may have dependencies on other packages and may be dependencies themselves. They may also include scripts that will be run directly. The opposite of a library package is an application package.
Library packages should not check their lockfile into source control, since they should support a range of dependency versions. Their immediate dependencies’ version constraints should be as wide as possible while still ensuring that the dependencies will be compatible with the versions that were tested against.
Since semantic versioning requires that libraries increment
their major version numbers for any backwards incompatible changes, library
packages will usually require their dependencies’ versions to be greater than or
equal to the versions that were tested and less than the next major version. So
if your library depended on the (fictional)
transmogrify package and you
tested it at version 1.2.1, your version constraint would be
A file named
pubspec.lock that specifies the concrete versions and other
identifying information for every immediate and transitive dependency a package
Unlike the pubspec, which only lists immediate dependencies and allows version ranges, the lock file comprehensively pins down the entire dependency graph to specific versions of packages. A lockfile ensures that you can recreate the exact configuration of packages used by an application.
The lockfile is generated automatically for you by pub when you run
pub get or
pub upgrade. If your
package is an application package, you will typically check this into source
control. For library packages, you usually won’t.
The declared versions of the Dart SDK itself that a package declares that it supports. An SDK constraint is specified using normal version constraint syntax, but in a special “environment” section in the pubspec.
A kind of place that pub can get packages from. A source isn’t a specific place like pub.dartlang.org or some specific Git URL. Each source describes a general procedure for accessing a package in some way. For example, “git” is one source. The git source knows how to download packages given a Git URL. There are a few different supported sources.
When pub gets a remote package, it downloads it into a single “system cache”
directory maintained by pub. When it generates a “packages” directory for a
package, that only contains symlinks to the real packages in the system cache.
On Mac and Linux, this directory defaults to
~/.pub-cache. On Windows, it
This means you only have to download a given version of a package once and can then reuse it in as many packages as you would like. It also means you can delete and regenerate your “packages” directory without having to access the network.
A transformer is a Dart object that converts input assets (such as
and HTML). The
pub build command puts the generated assets
into files. The
pub serve command, on the other hand,
doesn’t produce files; its generated assets are served directly by the dev
A dependency that your package indirectly uses because one of its dependencies requires it. If your package depends on A, which in turn depends on B which depends on C, then A is an immediate dependency and B and C are transitive ones.
An uploader of a package is someone who has administrative permissions for that package. They can not only upload new versions of a package, but also add and remove other uploaders for that package. The uploader of a package is often, but not necessarily, the same as the author of a package.
Anyone uploading a new package automatically becomes an uploader for that package. Otherwise, to become an uploader, you need to contact an existing uploader and ask them to add you as another uploader.
A constraint placed on each dependency of a package that
specifies which versions of that dependency the package is expected to work
with. This can be a single version (e.g.
0.3.0), a range of versions (e.g.
">=1.2.1 <2.0.0"), or
any (or just empty) to specify that any version is
Library packages should always specify version constraints for all of their dependencies, but application packages should usually allow any version of their dependencies, since they use the lockfile to manage their dependency versions.