pl-lens

This Rust library provides support for lenses, which are a mechanism in functional programming for focusing on a part of a complex data structure.

Usage

Add a dependency to your Cargo.toml:

toml [dependencies] pl-lens = "1.0"

Then, in your crate:

``rust // To use thederive(Lenses)` macro use pl_lens::Lenses;

// To use the lens! macro use pl_lens::lens;

// To bring trait methods like get_ref and set into scope use pl_lens::{Lens, RefLens}; ```

Examples

A Lens can be used to transform a conceptually-immutable data structure by changing only a portion of the data. Let's demonstrate with an example:

```rust

[derive(Lenses)]

struct Address { street: String, city: String, postcode: String }

[derive(Lenses)]

struct Person { name: String, age: u8, address: Address }

let p0 = Person { name: "Pop Zeus".tostring(), age: 58, address: Address { street: "123 Needmore Rd".tostring(), city: "Dayton".tostring(), postcode: "99999".tostring() } }; asserteq!(lens!(Person.name).getref(&p0), "Pop Zeus"); asserteq!(lens!(Person.address.street).getref(&p0), "123 Needmore Rd");

let p1 = lens!(Person.address.street).set(p0, "666 Titus Ave".tostring()); asserteq!(lens!(Person.name).getref(&p1), "Pop Zeus"); asserteq!(lens!(Person.address.street).get_ref(&p1), "666 Titus Ave"); ```

License

pl-lens is distributed under an MIT license. See LICENSE for more details.