struct Foo { int a; }
struct Foo2 { int a; }
struct Foo3 { int a; }
struct Bar { int a; }

fn int Foo.x(&self, int x) @operator([]) => 1;
fn int Foo.y(&self, int x) @operator(&[]) => 1;        // #error: The return type must be a pointer
fn int Foo2.y(&self, int x) @operator([]) => null;
fn int** Foo2.y2(&self, int x) @operator(&[]) => null; // #error: There is a mismatch of the 'value' type

fn int Foo3.x(&self, int x) @operator([]) => 1;
fn void Foo3.z(&self, uint x, int a) @operator([]=) {}  // #error: There is a mismatch of the 'index'

fn double Bar.x(&self, int x) @operator([]) => 0.1;
fn void Bar.y(&self, int x, float y) @operator([]=) {} // #error: There is a mismatch of the 'value'
