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<b>pack-io-derive</b>
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<sup>PROCEDURAL MACROS FOR pack-io</sup>
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<p>
Procedural macros for <a href="https://crates.io/crates/pack-io"><code>pack-io</code></a>. Provides <code>#[derive(Serialize)]</code>, <code>#[derive(Deserialize)]</code>, and <code>#[derive(DeserializeView)]</code> for any struct (named, tuple, unit) and any enum.
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<strong>This crate is not intended to be used directly.</strong> Add <code>pack-io</code> to your <code>Cargo.toml</code> with the <code>derive</code> feature enabled instead — the macros are re-exported at <code>pack_io::{Serialize, Deserialize, DeserializeView}</code> and pulled in automatically.
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## Installation
Don't depend on `pack-io-derive` directly. Depend on `pack-io` with the `derive` feature:
```toml
[dependencies]
pack-io = { version = "0.4", features = ["derive"] }
```
## What the macros do
Three derives, all working on structs (named-field, tuple, unit) and enums (any variant shape), generic over type parameters:
```rust
use pack_io::{Serialize, Deserialize, DeserializeView};
#[derive(Serialize, Deserialize)]
struct Account {
id: u64,
handle: String,
active: bool,
}
#[derive(Serialize, Deserialize)]
enum Event {
Heartbeat,
Login { user: u64, ip: String },
Error(u32, String),
}
#[derive(DeserializeView)]
struct AccountView<'a> {
id: u64,
handle: &'a str, // borrows directly from the input buffer
active: bool,
}
```
| `Serialize` | `pack_io::Serialize` | Generic over the `pack_io::Encode` behaviour trait. |
| `Deserialize` | `pack_io::Deserialize` | Generic over the `pack_io::Decode` behaviour trait. Owning decode. |
| `DeserializeView` | `pack_io::DeserializeView<'a>` | Zero-copy. Struct must have exactly one lifetime parameter. |
Generated code is generic over `Encode` / `Decode`, so the same impl drives both the in-memory codec and the streaming `IoEncoder<W>` / `IoDecoder<R>` in the parent crate.
Field order in the source code is the encoded byte order. For enums, a `varint(variant_index)` prefix is emitted first, in source-declaration order starting at `0`. **Append new variants to the end** of an enum declaration to keep the wire shape backward-compatible — inserting in the middle shifts every later variant's index.
See the full [wire-format specification](https://github.com/jamesgober/pack-io/blob/main/docs/WIRE_FORMAT.md) and the [API reference](https://github.com/jamesgober/pack-io/blob/main/docs/API.md) in the parent repository.
## Compatibility
- **MSRV**: Rust 1.85 (2024 edition).
- **Version pinning**: `pack-io` depends on `pack-io-derive` with an exact `=X.Y.Z` constraint so mismatched derive output cannot leak across `pack-io` revisions.
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<div id="license">
<h2>License</h2>
<p>Licensed under either of</p>
<ul>
<li><b>Apache License, Version 2.0</b> — see <a href="../LICENSE-APACHE">LICENSE-APACHE</a> (<a href="http://www.apache.org/licenses/LICENSE-2.0" target="_blank">http://www.apache.org/licenses/LICENSE-2.0</a>)</li>
<li><b>MIT License</b> — see <a href="../LICENSE-MIT">LICENSE-MIT</a> (<a href="http://opensource.org/licenses/MIT" target="_blank">http://opensource.org/licenses/MIT</a>)</li>
</ul>
<p>at your option. Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.</p>
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<sup>COPYRIGHT <small>©</small> 2026 <strong>JAMES GOBER.</strong></sup>
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