From 7f88fe8790014f4c879ec49de4bfdb823043e16a Mon Sep 17 00:00:00 2001
From: Aleksey Kladov <aleksey.kladov@gmail.com>
Date: Tue, 6 Nov 2018 22:06:58 +0300
Subject: Add a pinch of comments

---
 crates/ra_syntax/src/ast/mod.rs | 4 ++++
 1 file changed, 4 insertions(+)

(limited to 'crates/ra_syntax/src/ast/mod.rs')

diff --git a/crates/ra_syntax/src/ast/mod.rs b/crates/ra_syntax/src/ast/mod.rs
index 4355531d0..d93f92672 100644
--- a/crates/ra_syntax/src/ast/mod.rs
+++ b/crates/ra_syntax/src/ast/mod.rs
@@ -12,6 +12,10 @@ use crate::{
     SyntaxNodeRef,
 };
 
+/// The main trait to go from untyped `SyntaxNode`  to a typed ast. The
+/// conversion itself has zero runtime cost: ast and syntax nodes have exactly
+/// the same representation: a pointer to the tree root and a pointer to the
+/// node itself.
 pub trait AstNode<'a>: Clone + Copy + 'a {
     fn cast(syntax: SyntaxNodeRef<'a>) -> Option<Self>
     where
-- 
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