Notes on using C++ package managers

Why do we need package management?

Why do we need a package manager other than the one your OS provides?

describe potential package variants and optional components: distros usually build one variant that is designed to work together with all other system components (the purpose of using OS distributions)
```
"encryption": [False, "openssl", "mbedtls"],
```
install multiple variants of the same library - different version, different dependencies, etc. - and configure the dynamic loader to find the one you need

Why do we need multi-platform package management?

set platform specific compiler flags e.g -fPIC doesn’t exist on Windows:

    if self.settings.os == "Windows":
        del self.options.fPIC

some libraries don’t support all platforms:

    if self.settings.os == 'Windows':
        self.build_requires("winflexbison/2.5.24")
    else:
        self.build_requires("bison/3.7.6")

install packages in a platform-independent way
```
conan install --requires=zlib/1.2.13
```

What is not the purpose of a package manager:

managing development tooling - but I want my gdb to read symbols from zlib 1.2.13
describing how-to build software - the great overlap

The problem: Where can we set compiler flags?

What do we need to build a binary? Where can we set compiler flags? Where to store these configuration files?

Aligning build configuration across several repositories is hard.

Conan as a package manager has overlapping functionality with other tools:

containers - Somewhat independent environment, can instruct the dynamic loader but uses the host system too
vm descriptions (ansible) - Can describe dependencies, but not all. Age old question: What do we consider “part of the environment” and what is managed by Conan.
build systems - We need to remove -fpic but keep other flags intact.

How we use Conan:

describe compile-time dependencies, package libraries, upload/download binary artifacts
describe runtime dependencies - build OS specific package format.

#cpp