Function Example

cel/cel_example_test.go:27–72

()

)

func Example() {
	// Create the CEL environment with declarations for the input attributes and the extension functions.
	// In many cases the desired functionality will be present in a built-in function.
	e, err := cel.NewEnv(
		// Variable identifiers used within this expression.
		cel.Variable("i", cel.StringType),
		cel.Variable("you", cel.StringType),
		// Function to generate a greeting from one person to another: i.greet(you)
		cel.Function("greet",
			cel.MemberOverload("string_greet_string", []*cel.Type{cel.StringType, cel.StringType}, cel.StringType,
				cel.BinaryBinding(func(lhs, rhs ref.Val) ref.Val {
					return types.String(fmt.Sprintf("Hello %s! Nice to meet you, I'm %s.\n", rhs, lhs))
				}),
			),
		),
	)
	if err != nil {
		log.Fatalf("environment creation error: %s\n", err)
	}

	// Compile the expression.
	ast, iss := e.Compile("i.greet(you)")
	if iss.Err() != nil {
		log.Fatalln(iss.Err())
	}

	// Create the program.
	prg, err := e.Program(ast)
	if err != nil {
		log.Fatalf("program creation error: %s\n", err)
	}

	// Evaluate the program against some inputs. Note: the details return is not used.
	out, _, err := prg.Eval(map[string]any{
		// Native values are converted to CEL values under the covers.
		"i": "CEL",
		// Values may also be lazily supplied.
		"you": func() ref.Val { return types.String("world") },
	})
	if err != nil {
		log.Fatalf("runtime error: %s\n", err)
	}

	fmt.Println(out)
	// Output:Hello world! Nice to meet you, I'm CEL.
}

func Example_globalOverload() {
	// The GlobalOverload example demonstrates how to define global overload function.