Trait derive_visitor::Visitor[−][src]

pub trait Visitor {
    fn visit(&mut self, item: &dyn Any, event: Event);
}
Expand description

An interface for visiting arbitrary data structures.

A visitor receives items that implement Any, and can use dynamic dispatch to downcast them to particular types that it is interested in. In the classal visitor pattern, a Visitor has a set of separate methods to deal with each particular item type. This behavior can be implemented automatically using derive.

Derivable

This trait can be derived for any struct or enum. By default, the derived implementation does nothing. You need to explicitly specify what item types and / or events your visitor is interested in, using top-level attribute:

ⓘ
#[derive(Visitor)]
#[visitor(Directory, File)]
struct NameValidator {
    errors: Vec<InvalidNameError>,
}

impl NameValidator {
    fn enter_directory(&mut self, item: &Directory) {
        // ...your logic here
    }
    fn exit_directory(&mut self, item: &Directory) {
        // ...your logic here
    }
    fn enter_file(&mut self, item: &File) {
        // ...your logic here
    }
    fn exit_file(&mut self, item: &File) {
        // ...your logic here
    }
}

Macro attributes

If your visitor is only interested in entering or exiting a particular type, but not both, you can configure the derived implementation to only call enter / exit, respectively:

ⓘ
#[derive(Visitor)]
#[visitor(Directory(enter), File(exit))]
struct NameValidator {
    errors: Vec<InvalidNameError>,
}

impl NameValidator {
    fn enter_directory(&mut self, item: &Directory) {
        // ...your logic here
    }
    fn exit_file(&mut self, item: &File) {
        // ...your logic here
    }
}

You can also provide custom method names for each type / event:

ⓘ
#[derive(Visitor)]
#[visitor(Directory(enter="custom_enter_directory", exit="custom_exit_directory"), File)]
struct NameValidator {
    errors: Vec<InvalidNameError>,
}

impl NameValidator {
    fn custom_enter_directory(&mut self, item: &Directory) {
        // ...your logic here
    }
    fn custom_exit_directory(&mut self, item: &Directory) {
        // ...your logic here
    }
    fn enter_file(&mut self, item: &File) {
        // ...your logic here
    }
    fn exit_file(&mut self, item: &File) {
        // ...your logic here
    }
}

Required methods

Implementors