49 lines
1.3 KiB
Markdown
49 lines
1.3 KiB
Markdown
Custom Type Indexers
|
|
===================
|
|
|
|
{{#include ../links.md}}
|
|
|
|
A custom type can also expose an _indexer_ by registering an indexer function.
|
|
|
|
A custom type with an indexer function defined can use the bracket '`[]`' notation to get a property value.
|
|
|
|
Like getters and setters, indexers take a `&mut` reference to the first parameter.
|
|
|
|
Indexers are disabled when the [`no_index`] feature is used.
|
|
|
|
For efficiency reasons, indexers **cannot** be used to overload (i.e. override) built-in indexing operations for
|
|
[arrays] and [object maps].
|
|
|
|
```rust
|
|
#[derive(Clone)]
|
|
struct TestStruct {
|
|
fields: Vec<i64>
|
|
}
|
|
|
|
impl TestStruct {
|
|
fn get_field(&mut self, index: i64) -> i64 {
|
|
self.fields[index as usize]
|
|
}
|
|
fn set_field(&mut self, index: i64, value: i64) {
|
|
self.fields[index as usize] = value
|
|
}
|
|
|
|
fn new() -> Self {
|
|
TestStruct { fields: vec![1, 2, 3, 4, 5] }
|
|
}
|
|
}
|
|
|
|
let mut engine = Engine::new();
|
|
|
|
engine
|
|
.register_type::<TestStruct>()
|
|
.register_fn("new_ts", TestStruct::new)
|
|
// Shorthand: .register_indexer_get_set(TestStruct::get_field, TestStruct::set_field);
|
|
.register_indexer_get(TestStruct::get_field)
|
|
.register_indexer_set(TestStruct::set_field);
|
|
|
|
let result = engine.eval::<i64>("let a = new_ts(); a[2] = 42; a[2]")?;
|
|
|
|
println!("Answer: {}", result); // prints 42
|
|
```
|