# pl-hlist
[](https://travis-ci.com/plausiblelabs/hlist-rs)
This Rust library provides support for heterogeneous lists (known as `HList`s). An `HList` is a functional,
tuple-like, strongly-typed data structure that can contain elements of differing types.
There are three layers in this library:
- A basic `HList` data structure consisting of `HCons` and `HNil` types.
- An `hlist!` macro for constructing an `HList` from a series of elements.
- An `HListSupport` plugin/attribute that, when declared for a struct, allows for easy conversion
of struct instances to/from an `HList` representation.
See the next section for more details on usage of these layers.
## Usage
Add a dependency to your `Cargo.toml`:
```toml
[dependencies]
pl-hlist = "1.0.0"
```
Then, in your crate:
```rust
use pl_hlist::*;
```
An `HList` can be constructed manually as follows:
```rust
let x: HCons<u8, HCons<u32, HNil>> = HCons(1u8, HCons(666u32, HNil));
```
The `hlist!` macro provides a convenient shorthand for constructing an `HList`:
```rust
let x: HCons<u8, HCons<u32, HNil>> = hlist!(1u8, 666u32);
```
The custom `HListSupport` derive attribute can be applied to a struct declaration to automatically implement support for converting that struct to/from an `HList` representation:
```rust
#[derive(HListSupport)]
struct TestStruct {
foo: u8,
bar: u32
}
let hlist0 = hlist!(1u8, 666u32);
let s = TestStruct::from_hlist(hlist0);
assert_eq!(s.foo, 1u8);
assert_eq!(s.bar, 666u32);
let hlist1 = s.into_hlist();
assert_eq!(hlist0, hlist1);
```
# License
`pl-hlist` is distributed under an MIT license. See LICENSE for more details.