53 lines
1.2 KiB
Markdown
53 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 of [`Engine`]'s evaluation/consuming 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 during an evaluation, use the `throw` keyword.
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```rust
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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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`Err(Box<EvalAltResult::ErrorRuntime(value, position)>)` with the exception value
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captured by `value`.
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```rust
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let result = engine.eval::<i64>(r#"
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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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"#);
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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`]({{rootUrl}}/language/try-catch.md)
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statement common to many C-like languages.
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```rust
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try
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{
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throw 42;
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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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