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// Licensed to the Apache Software Foundation (ASF) under one
// or more contributor license agreements. See the NOTICE file
// distributed with this work for additional information
// regarding copyright ownership. The ASF licenses this file
// to you under the Apache License, Version 2.0 (the
// "License"); you may not use this file except in compliance
// with the License. You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing,
// software distributed under the License is distributed on an
// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
// KIND, either express or implied. See the License for the
// specific language governing permissions and limitations
// under the License.
//! The internal implement details of OpenDAL.
//!
//! OpenDAL has provides unified abstraction via two-level API sets:
//!
//! - Public API like [`Operator`] provides user level API.
//! - Raw API like [`Access`], [`Layer`] provides developer level API.
//!
//! OpenDAL tries it's best to keep the public API stable. But raw APIs
//! may change between minor releases from time to time. So most users
//! should only use the public API. And only developers need to implement
//! with raw API to implement a new service [`Access`] or their own
//! [`Layer`].
//!
//! In this section, we will talk about the following components:
//!
//! - [`Access`][accessor]: to connect underlying storage services.
//! - [`Layer`][layer]: middleware/interceptor between storage services.
//!
//! The relation between [`Access`], [`Layer`] and [`Operator`] looks like the following:
//!
//! ```text
//! ┌─────────────────────────────────────────────────┬──────────┐
//! │ │ │
//! │ ┌──────────┐ ┌────────┐ │ │
//! │ │ │ │ ▼ │ │
//! │ s3──┐ │ │ │ Tracing Layer │ │
//! │ │ │ │ │ │ │ │
//! │ gcs──┤ │ │ │ ▼ │ │
//! │ ├──►│ Accessor ├──┘ Metrics Layer ┌───►│ Operator │
//! │ azblob──┤ │ │ │ │ │ │
//! │ │ │ │ ▼ │ │ │
//! │ hdfs──┘ │ │ Logging Layer │ │ │
//! │ │ │ │ │ │ │
//! │ └──────────┘ └──────┘ │ │
//! │ │ │
//! └─────────────────────────────────────────────────┴──────────┘
//! ```
//!
//! [`Builder`]: crate::Builder
//! [`Operator`]: crate::Operator
//! [`Access`]: crate::raw::Access
//! [`Layer`]: crate::raw::Layer