60 lines
1.6 KiB
Markdown
60 lines
1.6 KiB
Markdown
Make a Custom Type Iterable
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===========================
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{{#include ../links.md}}
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```admonish info.side "Built-in type iterators"
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Type iterators are already defined for built-in [standard types] such as [strings], [ranges],
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[bit-fields], [arrays] and [object maps].
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That's why they can be used with the [`for`] loop.
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```
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If a [custom type] is iterable, the [`for`] loop can be used to iterate through
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its items in sequence, as long as it has a _type iterator_ registered.
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`Engine::register_iterator<T>` allows registration of a type iterator for any type
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that implements `IntoIterator`.
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With a type iterator registered, the [custom type] can be iterated through.
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```rust
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// Custom type
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#[derive(Debug, Clone)]
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struct TestStruct { fields: Vec<i64> }
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// Implement 'IntoIterator' trait
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impl IntoIterator<Item = i64> for TestStruct {
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type Item = i64;
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type IntoIter = std::vec::IntoIter<Self::Item>;
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fn into_iter(self) -> Self::IntoIter {
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self.fields.into_iter()
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}
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}
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let mut engine = Engine::new();
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// Register API and type iterator for 'TestStruct'
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engine.register_type_with_name::<TestStruct>("TestStruct")
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.register_fn("new_ts", || TestStruct { fields: vec![1, 2, 3, 42] })
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.register_iterator::<TestStruct>();
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// 'TestStruct' is now iterable
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engine.run(
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"
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for value in new_ts() {
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...
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}
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")?;
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```
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```admonish tip.small "Tip: Fallible type iterators"
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`Engine::register_iterator_result` allows registration of a _fallible_ type iterator –
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i.e. an iterator that returns `Result<T, Box<EvalAltResult>>`.
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On in very rare situations will this be necessary though.
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```
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