How Do I Use Other Libraries as Dependencies?

Of course, fundamental to any build system is the question of consuming dependencies. bpt takes an approach that is both familiar and novel.

The Familiar:

Dependencies are listed in a project’s manifest file (bpt.yaml, for bpt).

A range of acceptable versions is provided in the project manifest, which tells bpt and your consumers what versions of a particular dependency are allowed to be used with your package.

Transitive dependencies are resolved and pulled the same as if they were listed in the manifest as well.

The Novel:

bpt does not have a separate “install” step. Instead, whenever a bpt build is executed, the dependencies are resolved, downloaded, extracted, and compiled. Of course, bpt caches every step of this process, so you’ll only see the download, extract, and compilation when you add a new dependency,

Additionally, changes in the toolchain will necessitate that all the dependencies be re-compiled. Since the compilation of dependencies happens alongside the main project, the same caching layer that provides incremental compilation to your own project will be used to perform incremental compilation of your dependencies as well.

Listing Package Dependencies

Suppose you have a project and you wish to use spdlog for your logging. To begin, we need to find a spdlog package. We can search via bpt pkg search:

$ bpt pkg search spdlog
    Name: spdlog
Versions: 1.4.0, 1.4.1, 1.4.2, 1.5.0, 1.6.0, 1.6.1, 1.7.0, 1.8.0, 1.8.1,
          1.8.2, 1.8.3, 1.8.4, 1.8.5, 1.9.0, 1.9.1, 1.9.2

In the output above, we can see one spdlog group with several available versions. Let’s pick the newest available, 1.9.2.

If you’ve followed at least the Hello, World tutorial, you should have at least a bpt.yaml file present. Dependencies are listed in the bpt.yaml file under the dependencies key as a list of dependency statement strings:

name: my-application
version: 1.2.3
  - spdlog@1.9.2 using spdlog

The string "spdlog@1.9.2" is a dependency statement, and says that we want spdlog, with minimum version 1.9.2, but less than version 2.0.0. Refer to Compatible Range Specifiers for information on the version range syntax.

The using spdlog suffix declares that we want to use the spdlog libraries within the package. This will attach the spdlog/spdlog library to the libraries within our own project.

Using Dependencies

We’ve prepared our bpt.yaml so how do we get the dependencies and use them in our code?

Simply use them. There is no separate “install” step. Write your application as normal:

#include <spdlog/spdlog.h>

int main() {
  spdlog::info("Hello, dependency!");

Now when you run bpt build, you’ll see bpt automatically download spdlog as well as fmt (a dependency of spdlog), and then build all three components simultaneously. The result will be an app executable that uses spdlog.