// Copyright 2019 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package p

type List[E any] []E
var _ List[List[List[int]]]
var _ List[List[List[int]]] = []List[List[int]]{}

type (
	T1[P1 any] struct {
		f1 T2[P1, float32]
	}

	T2[P2, P3 any] struct {
		f2 P2
		f3 P3
	}
)

func _() {
	var x1 T1[int]
	var x2 T2[int, float32]

	x1.f1.f2 = 0
	x1.f1 = x2
}

type T3[P any] T1[T2[P, P]]

func _() {
	var x1 T3[int]
	var x2 T2[int, int]
	x1.f1.f2 = x2
}

func f[P any] (x P) List[P] {
	return List[P]{x}
}

var (
	_ []int = f(0)
	_ []float32 = f[float32](10)
	_ List[complex128] = f(1i)
	_ []List[int] = f(List[int]{})
        _ List[List[int]] = []List[int]{}
        _ = []List[int]{}
)

// Parameterized types with methods

func (l List[E]) Head() (_ E, _ bool) {
	if len(l) > 0 {
		return l[0], true
	}
	return
}

// A test case for instantiating types with other types (extracted from map.go2)

type Pair[K any] struct {
	key K
}

type Receiver[T any] struct {
	values T
}

type Iterator[K any] struct {
	r Receiver[Pair[K]]
}

func Values [T any] (r Receiver[T]) T {
        return r.values
}

func (it Iterator[K]) Next() K {
        return Values[Pair[K]](it.r).key
}

// A more complex test case testing type bounds (extracted from linalg.go2 and reduced to essence)

type NumericAbs[T any] interface {
	Abs() T
}

func AbsDifference[T NumericAbs[T]](x T)

type OrderedAbs[T any] T

func (a OrderedAbs[T]) Abs() OrderedAbs[T]

func OrderedAbsDifference[T any](x T) {
	AbsDifference(OrderedAbs[T](x))
}

// same code, reduced to essence

func g[P interface{ m() P }](x P)

type T4[P any] P

func (_ T4[P]) m() T4[P]

func _[Q any](x Q) {
	g(T4[Q](x))
}

// Another test case that caused  problems in the past

type T5[_ interface { a() }, _ interface{}] struct{}

type A[P any] struct{ x P }

func (_ A[P]) a() {}

var _ T5[A[int], int]

// Invoking methods with parameterized receiver types uses
// type inference to determine the actual type arguments matching
// the receiver type parameters from the actual receiver argument.
// Go does implicit address-taking and dereferenciation depending
// on the actual receiver and the method's receiver type. To make
// type inference work, the type-checker matches "pointer-ness"
// of the actual receiver and the method's receiver type.
// The following code tests this mechanism.

type R1[A any] struct{}
func (_ R1[A]) vm()
func (_ *R1[A]) pm()

func _[T any](r R1[T], p *R1[T]) {
	r.vm()
	r.pm()
	p.vm()
	p.pm()
}

type R2[A, B any] struct{}
func (_ R2[A, B]) vm()
func (_ *R2[A, B]) pm()

func _[T any](r R2[T, int], p *R2[string, T]) {
	r.vm()
	r.pm()
	p.vm()
	p.pm()
}

// Interface type constraints can contain any type, incl. *Named types.
// Verify that we use the underlying type to compute the operational type.
type MyInt int
func add1[T interface{ ~MyInt }](x T) T {
	return x + 1
}

type MyString string
func double[T interface{ ~MyInt | ~MyString }](x T) T {
	return x + x
}

// Embedding of interfaces with type constraints leads to interfaces
// with type constraints that are the intersection of the embedded
// type constraints.

type E0 interface {
	~int | ~bool | ~string
}

type E1 interface {
	~int | ~float64 | ~string
}

type E2 interface {
	~float64
}

type I0 interface {
	E0
}

func f0[T I0]()
var _ = f0[int]
var _ = f0[bool]
var _ = f0[string]
var _ = f0[float64 /* ERROR does not satisfy I0 */ ]

type I01 interface {
	E0
	E1
}

func f01[T I01]()
var _ = f01[int]
var _ = f01[bool /* ERROR does not satisfy I0 */ ]
var _ = f01[string]
var _ = f01[float64 /* ERROR does not satisfy I0 */ ]

type I012 interface {
	E0
	E1
	E2
}

func f012[T I012]()
var _ = f012[int /* ERROR does not satisfy I012 */ ]
var _ = f012[bool /* ERROR does not satisfy I012 */ ]
var _ = f012[string /* ERROR does not satisfy I012 */ ]
var _ = f012[float64 /* ERROR does not satisfy I012 */ ]

type I12 interface {
	E1
	E2
}

func f12[T I12]()
var _ = f12[int /* ERROR does not satisfy I12 */ ]
var _ = f12[bool /* ERROR does not satisfy I12 */ ]
var _ = f12[string /* ERROR does not satisfy I12 */ ]
var _ = f12[float64]

type I0_ interface {
	E0
	~int
}

func f0_[T I0_]()
var _ = f0_[int]
var _ = f0_[bool /* ERROR does not satisfy I0_ */ ]
var _ = f0_[string /* ERROR does not satisfy I0_ */ ]
var _ = f0_[float64 /* ERROR does not satisfy I0_ */ ]