🛠️ Impl Collection

[amimart]

💡 Purpose

The PR brings the implementation of the core Collection API.

⚙️ Details

Here's the functions implemented:

• collection::insert();
• collection::update();
• collection::save();
• collection::remove();
• collection::scan();

The arguments have been changed to borrowed values to avoid copy/clone.

The function's bodies are pretty basic, but some refactoring to allow zero-copy and zero-allocation behaviours were needed, especially concerning indexes traits, for instance regarding the Index::update() signature:

fn update<'a, DB: MultiStoreWriteHandle>(
        db: &mut DB,
        pk: &Record::Key<'a>,
        old: Option<&Record>,
        new: &'a Record,
    ) -> Result<(), Error>
    where
        for<'ik, 'pk> Self::Kind<'ik>: IndexKind<Self::Key<'ik>, Record::Key<'pk>>,

The main change here is the lifetime separation between the old record and the primary key, the reason lies in their provenance in the collection methods, for exemple with the update fn: The primary key is provided to collection::update() so its lifetime outlives its scope, but the old record is fetched in collection::update() so its lifetime is inferior to the primary key and the new value. This caused a necessary change in the indexKind::StoreKey<'ik, 'pk> to carry both lifetimes and thus, contaminating indexes api.

🧪 Testing

For testing purposes a mocked implementation of MultiStore has been introduced and allows to:

• Provide static data already present;
• Observes operations log;