57 lines
1.2 KiB
Markdown
57 lines
1.2 KiB
Markdown
Throw Exception on Error
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========================
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{{#include ../links.md}}
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All [`Engine`] evaluation API methods return `Result<T, Box<rhai::EvalAltResult>>`
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with `EvalAltResult` holding error information.
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To deliberately return an error, use the `throw` keyword.
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```js
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if some_bad_condition_has_happened {
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throw error; // 'throw' any value as the exception
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}
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throw; // defaults to '()'
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```
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Exceptions thrown via `throw` in the script can be captured in Rust by matching
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`EvalAltResult::ErrorRuntime(value, position)` with the exception value captured by `value`.
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```rust
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let result = engine.eval::<i64>(
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"
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let x = 42;
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if x > 0 {
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throw x;
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}
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").expect_err();
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println!("{result}"); // prints "Runtime error: 42 (line 5, position 15)"
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```
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Catch a Thrown Exception
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------------------------
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It is possible to _catch_ an exception instead of having it abort the evaluation
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of the entire script via the [`try` ... `catch`][`try`]
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statement common to many C-like languages.
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```js
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fn code_that_throws() {
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throw 42;
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}
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try
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{
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code_that_throws();
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}
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catch (err) // 'err' captures the thrown exception value
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{
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print(err); // prints 42
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}
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```
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