Module maomi::diff

The diff algorithm utilities.

When applying list update, the framework tries to figure out which items should be added, removed, or moved. For example, in the following component:

use maomi::prelude::*;
 
#[component]
struct MyComponent {
    template: template! {
        for item in self.list.iter() {
            /* ... */
        }
    },
    list: Vec<usize>,
}

This requires an algorithm to compare the current list and the list that used to do previous update, and decide which items should be added, removed, or moved.

By default, the keyless algorithm is used. This algorithm compares items one by one, and adds or removes items at the ends of the list. For example:

• if the list in the previous update is [30, 40, 50] while the current list is [30, 40, 50, 60] , then the forth item with item data 60 is added;
• if the list in the previous update is [30, 40, 50] while the current list is [30, 50] , then the second item is updated with item data 50 , and the third item is removed. This algorithm is very fast if the items at the start and the middle of the list will not be removed or inserted, but it is pretty slow if that happens.

For lists that often randomly changes, the key algorithm is a better option. To use this algorithm, the AsListKey trait must be implemented for the item data, and the use instruction should be added in the template for expression. The example code above should be changed:

use maomi::prelude::*;
 
struct ListData {
    id: usize,
}
 
impl AsListKey for ListData {
    type ListKey = usize;
 
    fn as_list_key(&self) -> &usize {
        &self.id
    }
}
 
#[component]
struct MyComponent {
    template: template! {
        // add a `use` list key
        for item in self.list.iter() use usize {
            /* ... */
        }
    },
    list: Vec<ListData>,
}

The ListKey is used for list comparison.

• if the ListKey list in the previous update is [30, 40, 50] while the current is [30, 50] , then the second item is removed.
• if the ListKey list in the previous update is [30, 40, 50] while the current is [30, 40, 60, 50] , then the third item with item data 60 is inserted; This algorithm has a balanced performance on lists that dynamically changes, while it has a small overhead no matter the list is changed or not.

Modules

• key
  The key list-update algorithm module.
• keyless
  The keyless list algorithm module.