documenting traits

docs/language_concepts/12_traits.md

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+---
+title: Traits
+description:
+  Learn how to write traits in Noir programming language. A trait is a group of methods that are defined for a particular type.
+keywords: [Noir programming language, traits, rust]
+---
+
+Traits in Noir work in [much the same way as in Rust](https://doc.rust-lang.org/book/ch10-02-traits.html). It's highly recommended that you get familiar with the concept of Traits in Rust, as it will help you understanding how they work in Noir.
+
+## Example
+
+First you need to define a Struct that will hold the implementation of a Trait. Example
+
+```rust
+struct Values {
+    x: Field,
+    y: Field,
+}
+```
+
+then define the trait:
+
+```rust
+trait Comparison {
+    fn eq(sf: Values, other: Values);
+}
+```
+
+and the implementation of that trait in your struct:
+
+```rust
+impl Comparison for Values {
+    fn eq(sf: Values, other: Values) {
+        assert((sf.x == other.x) & (sf.y == other.y));
+    }
+}
+```
+
+Now you should have a struct that implements the `Comparison` Trait. This means you can simply call `.eq()` on your struct:
+
+```rust
+fn main(x : Values, y : pub Values) {
+    x.eq(y);
+}
+```