A package which generates mutable and immutable *visiting* implementations for AST nodes.
A visitor is a implementor a trait of which the a function is called of a each node.
This module is specific for the *parser* module and contains the ability to extend with data.
## Usage
```rust
use visitable_derive::Visitable;
#[derive(Visitable)]
struct MyAstNode {
...
}
```
## Attributes
### `visit_self`
Will visit all fields **first then** self
```rust
#[derive(Visitable)]
#[visit_self]
struct MyAstNode {
...
}
```
Options:
- `also_visit_first_if`
Will visit self additionally before if predicate is true
```rust
#[derive(Visitable)]
#[visit_self(also_visit_first_if="self.predicate()"]
struct MyAstNode {
...
}
impl MyAstNode {
fn predicate(&self) -> bool {
...
}
}
```
### `visit_skip_field`
Skips visiting the field. Used if type does not implement `Visitable`
```rust
#[derive(Visitable)]
struct MyAstNode {
#[visit_skip_field]
a: String
}
```