42 lines
1.5 KiB
Markdown
42 lines
1.5 KiB
Markdown
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Register a Fallible Rust Function
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================================
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{{#include ../links.md}}
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If a function is _fallible_ (i.e. it returns a `Result<_, Error>`), it can be registered with `register_result_fn`
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(using the `RegisterResultFn` trait).
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The function must return `Result<Dynamic, Box<EvalAltResult>>`.
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`Box<EvalAltResult>` implements `From<&str>` and `From<String>` etc.
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and the error text gets converted into `Box<EvalAltResult::ErrorRuntime>`.
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The error values are `Box`-ed in order to reduce memory footprint of the error path, which should be hit rarely.
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```rust
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use rhai::{Engine, EvalAltResult, Position};
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use rhai::RegisterResultFn; // use 'RegisterResultFn' trait for 'register_result_fn'
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// Function that may fail - the result type must be 'Dynamic'
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fn safe_divide(x: i64, y: i64) -> Result<Dynamic, Box<EvalAltResult>> {
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if y == 0 {
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// Return an error if y is zero
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Err("Division by zero!".into()) // short-cut to create Box<EvalAltResult::ErrorRuntime>
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} else {
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Ok((x / y).into()) // convert result into 'Dynamic'
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}
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}
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fn main()
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{
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let engine = Engine::new();
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// Fallible functions that return Result values must use register_result_fn()
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engine.register_result_fn("divide", safe_divide);
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if let Err(error) = engine.eval::<i64>("divide(40, 0)") {
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println!("Error: {:?}", *error); // prints ErrorRuntime("Division by zero detected!", (1, 1)")
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}
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}
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```
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