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Support Dynamic return values.

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Stephen Chung
2020-04-13 10:27:08 +08:00
parent adaf086e90
commit 5796e520ec
5 changed files with 82 additions and 70 deletions
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README.md
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@@ -180,13 +180,18 @@ fn main() -> Result<(), EvalAltResult>
### Script evaluation
The type parameter is used to specify the type of the return value, which _must_ match the actual type or an error is returned.
Rhai is very strict here. There are two ways to specify the return type - _turbofish_ notation, or type inference.
Rhai is very strict here. Use [`Dynamic`] for uncertain return types.
There are two ways to specify the return type - _turbofish_ notation, or type inference.
```rust
let result = engine.eval::<i64>("40 + 2")?; // return type is i64, specified using 'turbofish' notation
let result: i64 = engine.eval("40 + 2")?; // return type is inferred to be i64
result.is::<i64>() == true;
let result: Dynamic = engine.eval("boo()")?; // use 'Dynamic' if you're not sure what type it'll be!
let result = engine.eval::<String>("40 + 2")?; // returns an error because the actual return type is i64, not String
```
@@ -440,7 +445,7 @@ function and match against the name).
A `Dynamic` value's actual type can be checked via the `is` method.
The `cast` method then converts the value into a specific, known type.
Alternatively, use the `try_cast` method which does not panic but returns an error when the cast fails.
Alternatively, use the `try_cast` method which does not panic but returns `None` when the cast fails.
```rust
let list: Array = engine.eval("...")?; // return type is 'Array'
@@ -451,7 +456,7 @@ item.is::<i64>() == true; // 'is' returns whether a 'Dynam
let value = item.cast::<i64>(); // if the element is 'i64', this succeeds; otherwise it panics
let value: i64 = item.cast(); // type can also be inferred
let value = item.try_cast::<i64>()?; // 'try_cast' does not panic when the cast fails, but returns an error
let value = item.try_cast::<i64>().unwrap(); // 'try_cast' does not panic when the cast fails, but returns 'None'
```
The `type_name` method gets the name of the actual type as a static string slice, which you may match against.