feat: add example3

__wasm/wasmtime/examples/example3.rs

@@ -0,0 +1,37 @@
+use anyhow::Result;
+use wasmtime::*;
+
+fn main() -> Result<()> {
+    // Modules can be compiled through either the text or binary format
+    let engine = Engine::default();
+    let wat = r#"
+        (module
+            (import "host" "hello" (func $host_hello (param i32)))
+
+            (func (export "hello")
+                i32.const 3
+                call $host_hello)
+        )
+    "#;
+    let module = Module::new(&engine, wat)?;
+
+    // Create a `Linker` which will be later used to instantiate this module.
+    // Host functionality is defined by name within the `Linker`.
+    let mut linker = Linker::new(&engine);
+    linker.func_wrap("host", "hello", |caller: Caller<'_, u32>, param: i32| {
+        println!("Got {} from WebAssembly", param);
+        println!("my host state is: {}", caller.data());
+    })?;
+
+    // All wasm objects operate within the context of a "store". Each
+    // `Store` has a type parameter to store host-specific data, which in
+    // this case we're using `4` for.
+    let mut store = Store::new(&engine, 4);
+    let instance = linker.instantiate(&mut store, &module)?;
+    let hello = instance.get_typed_func::<(), ()>(&mut store, "hello")?;
+
+    // And finally we can call the wasm!
+    hello.call(&mut store, ())?;
+
+    Ok(())
+}

__wasm/wasmtime/justfile

@@ -12,4 +12,6 @@ run_example1:
 run_example2:
   cargo run --example example2
 
+run_example3:
+  cargo run --example example3