[Discussion/refactor/rocks-lib] expose builders for operations

[mrcjkb]

Functions like operations::install take parameters that are often instantiated using a default value.
Perhaps we can use builders instead. This could make the API more flexible, allowing us to add optional arguments without it being a breaking change.

For example, operations::install could look like this:

Installer::new()
  .packages(...)
  .package_db(...)
  .config(...)
  .pin(...)
  .install()

Bonus: Since there are non-optional parameters, we could implement type-safe curried builders, where the types would look like this:

Installer::new() // => Installer
  .packages(...) // => InstallerWithPackages
  .package_db(...) // => InstallerWithPackageDB
  .config(...) // => InstallerReady
  .pin(...) // => InstallerReady (pin and progress are optional)
  .install()

Or, not as pretty, but simpler, with less boilerplate:

Installer::new(packages, package_db, conifg)
  .pin(...)
  .install()

In this example, all arguments could be optional (config has a default, package_db can be instantiated from a default config, packages can be empty...)

@vhyrro, what are your thoughts?