55 lines
1.6 KiB
Markdown
55 lines
1.6 KiB
Markdown
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Hello World in Rhai
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===================
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{{#include ../links.md}}
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To get going with Rhai is as simple as creating an instance of the scripting engine `rhai::Engine` via
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`Engine::new`, then calling the `eval` method:
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```rust
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use rhai::{Engine, EvalAltResult};
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fn main() -> Result<(), Box<EvalAltResult>>
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{
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let engine = Engine::new();
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let result = engine.eval::<i64>("40 + 2")?;
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// ^^^^^^^ cast the result to an 'i64', this is required
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println!("Answer: {}", result); // prints 42
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Ok(())
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}
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```
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`rhai::EvalAltResult` is a Rust `enum` containing all errors encountered during the parsing or evaluation process.
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Evaluate a Script
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----------------
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The type parameter is used to specify the type of the return value, which _must_ match the actual type or an error is returned.
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Rhai is very strict here.
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Use [`Dynamic`] for uncertain return types.
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There are two ways to specify the return type - _turbofish_ notation, or type inference.
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```rust
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let result = engine.eval::<i64>("40 + 2")?; // return type is i64, specified using 'turbofish' notation
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let result: i64 = engine.eval("40 + 2")?; // return type is inferred to be i64
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result.is::<i64>() == true;
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let result: Dynamic = engine.eval("boo()")?; // use 'Dynamic' if you're not sure what type it'll be!
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let result = engine.eval::<String>("40 + 2")?; // returns an error because the actual return type is i64, not String
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```
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Evaluate a script file directly:
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```rust
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let result = engine.eval_file::<i64>("hello_world.rhai".into())?; // 'eval_file' takes a 'PathBuf'
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```
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