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Update rust embed example (#967) (#968)

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* Update rust embed example (#967)

Ensures that the example works with the current API.
Drops mention of HostRef as the example is complete without it.

* Cleanup
This commit is contained in:
Gustav Eiman
2020-02-25 16:45:21 +01:00
committed by GitHub
parent f8abe1169c
commit 09a091802b
1 changed files with 12 additions and 17 deletions
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29
docs/embed-rust.md
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@@ -41,9 +41,6 @@ use wasmtime::*;
let store = Store::default();
```
The `HostRef` will be used a lot -- it is a "convenience" object to store and refer an object between the host and
the embedded environments.
The `hello.wasm` can be read from the file system and provided to the `Module` object constructor as `&[u8]`:
```rust
@@ -51,30 +48,28 @@ use std::fs::read;
let hello_wasm = read("hello.wasm").expect("wasm file");
let module = HostRef::new(Module::new(&store, &hello_wasm).expect("wasm module"));
let module = Module::new(&store, &hello_wasm).expect("wasm module");
```
The module instance can now be created. Normally, you would provide exports, but in this case, there are none required:
```rust
let instance = Instance::new(&store, &module, &[]).expect("wasm instance");
let instance = Instance::new(&module, &[]).expect("wasm instance");
```
Everything is set. If a WebAssembly module has a start function -- it was run.
The instance's exports can be used at this point. wasmtime provides functions
to look up an export by name, and ensure that it's a function:
to get an export by name, and ensure that it's a function:
```rust
let answer = instance.find_export_by_name("answer").expect("answer").func().expect("function");
let answer = instance.get_export("answer").expect("answer").func().expect("function");
```
The exported function can be called using the `call` method. Remember that in most of the cases,
a `HostRef<_>` object will be returned, so `borrow()` or `borrow_mut()` method has to be used to refer the
specific object. The exported "answer" function accepts no parameters and returns a single `i32` value.
The exported function can be called using the `call` method. The exported "answer" function accepts no parameters and returns a single `i32` value.
```rust
let result = answer.borrow().call(&[]).expect("success");
println!("Answer: {}", result[0].i32());
let result = answer.call(&[]).expect("success");
println!("Answer: {:?}", result[0].i32());
```
The names of the WebAssembly module's imports and exports can be discovered by means of module's corresponding methods.
@@ -90,11 +85,11 @@ fn main() {
let wasm = read("hello.wasm").expect("wasm file");
let module = HostRef::new(Module::new(&store, &wasm).expect("wasm module"));
let instance = Instance::new(&store, &module, &[]).expect("wasm instance");
let module = Module::new(&store, &wasm).expect("wasm module");
let instance = Instance::new(&module, &[]).expect("wasm instance");
let answer = instance.find_export_by_name("answer").expect("answer").func().expect("function");
let result = answer.borrow().call(&[]).expect("success");
println!("Answer: {}", result[0].i32());
let answer = instance.get_export("answer").expect("answer").func().expect("function");
let result = answer.call(&[]).expect("success");
println!("Answer: {:?}", result[0].i32());
}
```