class File(name: String) {
  def getName(): String = name
  def open() { /*..*/ }
  def close() { println("close file") }
}
def test(f: { def getName(): String }) { println(f.getName) }

test(new File("test.txt"))
test(new java.io.File("test.txt"))

XC>class File(name: String) {
XC>  def getName(): String = name
XC>  def open() { /*..*/ }
XC>  def close() { println("close file") }
XC>}
XC>def test(f: { def getName(): String }) { println(f.getName) }

XC>test(new File("test.txt"))
XC>test(new java.io.File("test.txt"))
XC>

prototype getName {};

def test[getName,...] {
   /*...*/
};

XC>def test(f: { def getName(): String }) { println(f.getName) }

XC>

void test(T f)
{
  BOOST_MPL_ASSERT((is_same< decltype(f.getName()), string >));
  cout << f.getName();
}

template<class T>
auto test(T f) -> typename enable_if<
                    is_same< decltype(f.getName()), string >
                  >::type
{
  cout << f.getName();
}

XC>class File(name: String) {
XC>  def getName(): String = name
XC>  def open() { /*..*/ }
XC>  def close() { println("close file") }
XC>}
XC>def test(f: { def getName(): String }) { println(f.getName) }

XC>test(new File("test.txt"))
XC>test(new java.io.File("test.txt"))
XC>

XC>В Go вроде бы тоже есть нечто подобное, но не нашел примера

package main

import "fmt"

type File struct {}
func (f File) getName() string {
  return "John"
}

func test(f interface{getName() string}) string {
  return f.getName()
}

func main() {
        var f File
    fmt.Println("Hello", test(f))
}

interface test_f_1f8sbdddx {
  getName() : string
}

def test(f: test_f_1f8sbdddx) { println(f.getName) }

T>>interface test_f_1f8sbdddx {
T>>  getName() : string
T>>}

T>>def test(f: test_f_1f8sbdddx) { println(f.getName) }
T>>

interface IFile {
  read() : bytes
  write(bytes)
  close()
}

f : IFile = open(...)
f.close()

f : interface <
  const _InterfaceName = "IFile"
  close()
> = open(...)
f.close()

var p : { x : Int, y : Int }; // declare a typed variable
p = { x : -1, y : 65 }; // OK
p = { x : -1 }; // ERROR : field y is missing

structural interface ITest
{
  ...
}

interface ITest
{
  int Method1(string s);
  string Prop1 { get; }
}

class A
{
  public Test(structural ITest test)
  {
    var x = test.Method1(test.Prop1);
    ...
  }
}
...
new A().Test(new B());

class ITest_Proxy
{
  public Func<string, int> Method1;
  public Func<string>      Prop1;
}

class A
{
  public Test(ITest test)
  {
    var x = test.Method1(test.Prop1);
    ...
  }
}
...
var tempB = new B();
var proxy = new ITest_Proxy() { tempB.Method1; tempB.Prop1; `}
new A().Test(proxy);

Т.е. будет нечто вроде:
template<class T>
auto MyInterface(T f)
  -> and_<
       is_same< decltype(f.getName()), string >,
       is_same< decltype(f.setName(string)), void >,
       // и т.д., остальные условия
     >::type;

template<class T>
void test(T f)
{
  BOOST_MPL_ASSERT((is_same< decltype(MyInterface(f)), true_ >));
  cout << f.getName();
}

#define CHECK_IFACE(iface) BOOST_MPL_ASSERT((is_same< decltype(iface), true_ >))

template<class T>
void test(T f)
{
  CHECK_IFACE(MyInterface(f));
  cout << f.getName();
}

#define CHECK_IFACE_RET(iface) typename enable_if< is_same< decltype(iface), true_ > >::type

template<class T>
auto test(T f) -> CHECK_IFACE_RET(MyInterface(f))
{
  cout << f.getName();
}

interface IShow
{
    string toString();
}

class Some
{
    string fileName() { return "1.txt"; }
}

interface IToString { string toString(); }

class MyData { string asString(); }
class MyData2 { list<char> toString(); }

VE>interface IToString { string toString(); }

VE>class MyData { string asString(); }
VE>class MyData2 { list<char> toString(); }
VE>

int CountChars(o)
{
return fold(enum(o.toString()), (sum, c) => sum + 1)
}

foo(myData { toString = asString })

let instance IsString MyData where
  toString = asString
in
  ...

class elephant = 
  object
    method say = printf "elephant\n"
  end

(* с точки зрения компилятора этот класс совпадает с elephant *)
class mamont = 
  object
    method say = printf "mamont\n"
  end


class dog = 
  object    
    method say = printf "dog\n"
    method dog_id = ()
  end

class wolf = 
  object
    method say = printf "wolf\n"
    method wolf_id = ()
  end


let elephant1_ = new elephant
let elephant2_ = new elephant
let mamont_ = new mamont
let dog_ = new dog
let wolf_ = new wolf