Merge pull request #358 from howjmay/ex-import-func

test: Add new example

examples/example_imports_exports_test.go

@@ -15,6 +15,7 @@ package wasmer
 
 import (
 	"fmt"
+
 	"github.com/wasmerio/wasmer-go/wasmer"
 )
 
@@ -98,7 +99,6 @@ func ExampleExtern() {
 	fmt.Println("Instantiating module...")
 	// Let's instantiate the Wasm module.
 	instance, err := wasmer.NewInstance(module, importObject)
-
 	if err != nil {
 		panic(fmt.Sprintln("Failed to instantiate the module:", err))
 	}

examples/example_imports_function_test.go

@@ -0,0 +1,139 @@
+// A Wasm module can import entities, like functions, memories,
+// globals and tables.
+//
+// This example illustrates how to use imported functions. They come
+// in 2 flavors:
+//
+//   1. Dynamic functions, where parameters and results are of a
+//      slice of `Value`,
+//   2. Native function, where parameters and results are statically
+//      typed Rust values.
+//
+// You can run the example directly by executing in Wasmer root:
+//
+// ```shell
+// go test examples/example_imports_function_test.go
+// ```
+//
+// Ready?
+
+package wasmer
+
+import (
+	"fmt"
+
+	"github.com/wasmerio/wasmer-go/wasmer"
+)
+
+func ExampleImportsFunction() {
+	// Let's declare the Wasm module.
+	//
+	// We are using the text representation of the module here.
+	wasmBytes := []byte(`
+	(module
+		(func $multiply_dynamic (import "env" "multiply_dynamic") (param i32) (result i32))
+		(func $multiply_typed (import "env" "multiply_typed") (param i32) (result i32))
+		(type $sum_t (func (param i32) (param i32) (result i32)))
+		(func $sum_f (type $sum_t) (param $x i32) (param $y i32) (result i32)
+		  (call $multiply_dynamic (local.get $x))
+		  (call $multiply_typed (local.get $y))
+		  i32.add)
+		(export "sum" (func $sum_f)))
+	`)
+
+	// Create an Engine
+	engine := wasmer.NewEngine()
+
+	// Create a Store
+	store := wasmer.NewStore(engine)
+
+	fmt.Println("Compiling module...")
+	module, err := wasmer.NewModule(store, wasmBytes)
+	if err != nil {
+		panic(fmt.Sprintln("Failed to compile module:", err))
+	}
+
+	// Here we go.
+	//
+	// Before we can instantiate our module, we need to define
+	// the entities we will import.
+	//
+	// We won't go into details here as creating entities will be
+	// covered in more detail in other examples.
+	fmt.Println("Creating the imported function...")
+	multiply_dynamic := wasmer.NewFunction(
+		store,
+		wasmer.NewFunctionType(wasmer.NewValueTypes(wasmer.I32), wasmer.NewValueTypes(wasmer.I32)),
+		func(args []wasmer.Value) ([]wasmer.Value, error) {
+			fmt.Println("Calling `multiply_dynamic`...")
+
+			result := args[0].I32() * 2
+			fmt.Println("Result of `multiply_dynamic`: ", result)
+
+			return []wasmer.Value{wasmer.NewI32(result)}, nil
+		},
+	)
+
+	type MyEnvironment struct{}
+
+	environment := MyEnvironment{}
+	multiply := func(environment interface{}, args []wasmer.Value) ([]wasmer.Value, error) {
+		fmt.Println("Calling `multiply_typed`...")
+		result := args[0].I32() * 3
+
+		fmt.Println("Result of `multiply_typed`: ", result)
+		return []wasmer.Value{wasmer.NewI32(result)}, nil
+	}
+	multiply_typed := wasmer.NewFunctionWithEnvironment(
+		store,
+		wasmer.NewFunctionType(wasmer.NewValueTypes(wasmer.I32), wasmer.NewValueTypes(wasmer.I32)),
+		environment,
+		multiply,
+	)
+
+	// Create an import object.
+	importObject := wasmer.NewImportObject()
+	importObject.Register(
+		"env",
+		map[string]wasmer.IntoExtern{
+			"multiply_dynamic": multiply_dynamic,
+			"multiply_typed":   multiply_typed,
+		},
+	)
+
+	fmt.Println("Instantiating module...")
+	// Let's instantiate the Wasm module.
+	instance, err := wasmer.NewInstance(module, importObject)
+	if err != nil {
+		panic(fmt.Sprintln("Failed to instantiate the module:", err))
+	}
+
+	// Here we go.
+	//
+	// The Wasm module exports a function called `sum`. Let's get it.
+	run, err := instance.Exports.GetFunction("sum")
+	if err != nil {
+		panic(fmt.Sprintln("Failed to retrieve the `run` function:", err))
+	}
+
+	result, err := run(1, 2)
+	if err != nil {
+		panic(fmt.Sprintln("`run` met error"))
+	}
+
+	fmt.Println("Results of `sum`:", result)
+
+	if result.(int32) != 8 {
+		panic("result is wrong")
+	}
+
+	// Output:
+	// Compiling module...
+	// Creating the imported function...
+	// Instantiating module...
+	// Calling `multiply_dynamic`...
+	// Result of `multiply_dynamic`:  2
+	// Calling `multiply_typed`...
+	// Result of `multiply_typed`:  6
+	// Results of `sum`: 8
+}