• Python

class Foo:
    def __init__(self, x, y):
        self.x = x
        self.y = y
    def __hash__(self):
        return hash((Foo, self.x, self.y))
    def __eq__(self, other):
        return (self.x, self.y) == (other.x, other.y)

foo = Foo(1, 2)
m = {foo: 'hello'}

• Python

class Foo:
    def __init__(self, value):
        self.value = value
    def __hash__(self):
        return hash(self.value)
    def __eq__(self, other):
        return self.value == other.value
m = {Foo(123): 'abc'}

• Python

class Foo:
    def __init__(self, value):
        self.value = value
    def __hash__(self):
        return hash(self.value)
    def __eq__(self, other):
        return self.value == other.value
class FooMap(dict):
    def __setitem__(self, key, value):
        key = Foo(key)
        super().__setitem__(key, value)
m = FooMap()
m[123] = ...
m['abc'] = ...
m[True] = ...

• Dart

class Foo{};
Map<Foo, int> m = {};

• Go

type Foo struct {
	name string
	x, y int
}

m := make(map[Foo]string)

• Lua

local map={[Foo]=true}

• Pascal

Type
  TMap = specialize TFPGMap<Foo, TData>;

• Perl

class Foo {
    has $x :param = 0;
}
 
my $p = Foo->new(x => 5);

my %map;

$map{$p} = 'some data';

• Perl

package Foo {    
    sub new { 
        my $class = shift; 
        return bless { @_ }, $class 
    }    
};
 
my $p = Foo->new(x => 5);

my %map;

$map{$p} = 'some data';

• Ruby

Foo = Struct.new(:x, :y)
m = {Foo.new(42, 5) => "Hello"}

• Rust

#[derive(Eq,PartialEq,Hash)]
struct Foo{}
let mut map = HashMap::<Foo, i32>::new();