libgo/go/go/types/testdata/check/typeparams.go2

// Copyright 2018 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

// import "io" // for type assertion tests

// The predeclared identifier "any" is only visible as a constraint
// in a type parameter list.
var _ any // ERROR undeclared
func _[_ any /* ok here */ , _ interface{any /* ERROR undeclared */ }](any /* ERROR undeclared */ ) {
        var _ any /* ERROR undeclared */
}

func identity[T any](x T) T { return x }

func _[_ any](x int) int
func _[T any](T /* ERROR redeclared */ T)()
func _[T, T /* ERROR redeclared */ any]()

// Constraints (incl. any) may be parenthesized.
func _[_ (any)]() {}
func _[_ (interface{})]() {}

func reverse[T any](list []T) []T {
        rlist := make([]T, len(list))
        i := len(list)
        for _, x := range list {
                i--
                rlist[i] = x
        }
        return rlist
}

var _ = reverse /* ERROR cannot use generic function reverse */
var _ = reverse[int, float32 /* ERROR got 2 type arguments */ ] ([]int{1, 2, 3})
var _ = reverse[int]([ /* ERROR cannot use */ ]float32{1, 2, 3})
var f = reverse[chan int]
var _ = f(0 /* ERROR cannot use 0 .* as \[\]chan int */ )

func swap[A, B any](a A, b B) (B, A) { return b, a }

var _ = swap /* ERROR single value is expected */ [int, float32](1, 2)
var f32, i = swap[int, float32](swap[float32, int](1, 2))
var _ float32 = f32
var _ int = i

func swapswap[A, B any](a A, b B) (A, B) {
        return swap[B, A](b, a)
}

type F[A, B any] func(A, B) (B, A)

func min[T interface{ type int }](x, y T) T {
        if x < y {
                return x
        }
        return y
}

func _[T interface{type int, float32}](x, y T) bool { return x < y }
func _[T any](x, y T) bool { return x /* ERROR cannot compare */ < y }
func _[T interface{type int, float32, bool}](x, y T) bool { return x /* ERROR cannot compare */ < y }

func _[T C1[T]](x, y T) bool { return x /* ERROR cannot compare */ < y }
func _[T C2[T]](x, y T) bool { return x < y }

type C1[T any] interface{}
type C2[T any] interface{ type int, float32 }

func new[T any]() *T {
        var x T
        return &x
}

var _ = new /* ERROR cannot use generic function new */
var _ *int = new[int]()

func _[T any](map[T /* ERROR incomparable map key type T \(missing comparable constraint\) */]int) // w/o constraint we don't know if T is comparable

func f1[T1 any](struct{T1}) int
var _ = f1[int](struct{T1}{})
type T1 = int

func f2[t1 any](struct{t1; x float32}) int
var _ = f2[t1](struct{t1; x float32}{})
type t1 = int


func f3[A, B, C any](A, struct{x B}, func(A, struct{x B}, *C)) int

var _ = f3[int, rune, bool](1, struct{x rune}{}, nil)

// indexing

func _[T any] (x T, i int) { _ = x /* ERROR "cannot index" */ [i] }
func _[T interface{ type int }] (x T, i int) { _ = x /* ERROR "cannot index" */ [i] }
func _[T interface{ type string }] (x T, i int) { _ = x[i] }
func _[T interface{ type []int }] (x T, i int) { _ = x[i] }
func _[T interface{ type [10]int, *[20]int, map[int]int }] (x T, i int) { _ = x[i] }
func _[T interface{ type string, []byte }] (x T, i int) { _ = x[i] }
func _[T interface{ type []int, [1]rune }] (x T, i int) { _ = x /* ERROR "cannot index" */ [i] }
func _[T interface{ type string, []rune }] (x T, i int) { _ = x /* ERROR "cannot index" */ [i] }

// indexing with various combinations of map types in type lists (see issue #42616)
func _[T interface{ type []E, map[int]E }, E any](x T, i int) { _ = x[i] }
func _[T interface{ type []E }, E any](x T, i int) { _ = &x[i] }
func _[T interface{ type map[int]E }, E any](x T, i int) { _, _ = x[i] } // comma-ok permitted
func _[T interface{ type []E, map[int]E }, E any](x T, i int) { _ = &x /* ERROR cannot take address */ [i] }
func _[T interface{ type []E, map[int]E, map[uint]E }, E any](x T, i int) { _ = x /* ERROR cannot index */ [i] } // different map element types
func _[T interface{ type []E, map[string]E }, E any](x T, i int) { _ = x[i /* ERROR cannot use i */ ] }

// slicing
// TODO(gri) implement this

func _[T interface{ type string }] (x T, i, j, k int) { _ = x /* ERROR invalid operation */ [i:j:k] }

// len/cap built-ins

func _[T any](x T) { _ = len(x /* ERROR invalid argument */ ) }
func _[T interface{ type int }](x T) { _ = len(x /* ERROR invalid argument */ ) }
func _[T interface{ type string, []byte, int }](x T) { _ = len(x /* ERROR invalid argument */ ) }
func _[T interface{ type string }](x T) { _ = len(x) }
func _[T interface{ type [10]int }](x T) { _ = len(x) }
func _[T interface{ type []byte }](x T) { _ = len(x) }
func _[T interface{ type map[int]int }](x T) { _ = len(x) }
func _[T interface{ type chan int }](x T) { _ = len(x) }
func _[T interface{ type string, []byte, chan int }](x T) { _ = len(x) }

func _[T any](x T) { _ = cap(x /* ERROR invalid argument */ ) }
func _[T interface{ type int }](x T) { _ = cap(x /* ERROR invalid argument */ ) }
func _[T interface{ type string, []byte, int }](x T) { _ = cap(x /* ERROR invalid argument */ ) }
func _[T interface{ type string }](x T) { _ = cap(x /* ERROR invalid argument */ ) }
func _[T interface{ type [10]int }](x T) { _ = cap(x) }
func _[T interface{ type []byte }](x T) { _ = cap(x) }
func _[T interface{ type map[int]int }](x T) { _ = cap(x /* ERROR invalid argument */ ) }
func _[T interface{ type chan int }](x T) { _ = cap(x) }
func _[T interface{ type []byte, chan int }](x T) { _ = cap(x) }

// range iteration

func _[T interface{}](x T) {
        for range x /* ERROR cannot range */ {}
}

func _[T interface{ type string, []string }](x T) {
        for range x {}
        for i := range x { _ = i }
        for i, _ := range x { _ = i }
        for i, e := range x /* ERROR must have the same element type */ { _ = i }
        for _, e := range x /* ERROR must have the same element type */ {}
        var e rune
        _ = e
        for _, (e) = range x /* ERROR must have the same element type */ {}
}


func _[T interface{ type string, []rune, map[int]rune }](x T) {
        for _, e := range x { _ = e }
        for i, e := range x { _ = i; _ = e }
}

func _[T interface{ type string, []rune, map[string]rune }](x T) {
        for _, e := range x { _ = e }
        for i, e := range x /* ERROR must have the same key type */ { _ = e }
}

func _[T interface{ type string, chan int }](x T) {
        for range x {}
        for i := range x { _ = i }
        for i, _ := range x { _ = i } // TODO(gri) should get an error here: channels only return one value
}

func _[T interface{ type string, chan<-int }](x T) {
        for i := range x /* ERROR send-only channel */ { _ = i }
}

// type inference checks

var _ = new /* ERROR cannot infer T */ ()

func f4[A, B, C any](A, B) C

var _ = f4 /* ERROR cannot infer C */ (1, 2)
var _ = f4[int, float32, complex128](1, 2)

func f5[A, B, C any](A, []*B, struct{f []C}) int

var _ = f5[int, float32, complex128](0, nil, struct{f []complex128}{})
var _ = f5 /* ERROR cannot infer */ (0, nil, struct{f []complex128}{})
var _ = f5(0, []*float32{new[float32]()}, struct{f []complex128}{})

func f6[A any](A, []A) int

var _ = f6(0, nil)

func f6nil[A any](A) int

var _ = f6nil /* ERROR cannot infer */ (nil)

// type inference with variadic functions

func f7[T any](...T) T

var _ int = f7 /* ERROR cannot infer T */ ()
var _ int = f7(1)
var _ int = f7(1, 2)
var _ int = f7([]int{}...)
var _ int = f7 /* ERROR cannot use */ ([]float64{}...)
var _ float64 = f7([]float64{}...)
var _ = f7[float64](1, 2.3)
var _ = f7(float64(1), 2.3)
var _ = f7(1, 2.3 /* ERROR does not match */ )
var _ = f7(1.2, 3 /* ERROR does not match */ )

func f8[A, B any](A, B, ...B) int

var _ = f8(1) /* ERROR not enough arguments */
var _ = f8(1, 2.3)
var _ = f8(1, 2.3, 3.4, 4.5)
var _ = f8(1, 2.3, 3.4, 4 /* ERROR does not match */ )
var _ = f8[int, float64](1, 2.3, 3.4, 4)

var _ = f8[int, float64](0, 0, nil...) // test case for #18268

// init functions cannot have type parameters

func init() {}
func init[/* ERROR func init must have no type parameters */ _ any]() {}
func init[/* ERROR func init must have no type parameters */ P any]() {}

type T struct {}

func (T) m1() {}
func (T) m2[ /* ERROR methods cannot have type parameters */ _ any]() {}
func (T) m3[ /* ERROR methods cannot have type parameters */ P any]() {}

// type inference across parameterized types

type S1[P any] struct { f P }

func f9[P any](x S1[P])

func _() {
        f9[int](S1[int]{42})
	f9(S1[int]{42})
}

type S2[A, B, C any] struct{}

func f10[X, Y, Z any](a S2[X, int, Z], b S2[X, Y, bool])

func _[P any]() {
        f10[int, float32, string](S2[int, int, string]{}, S2[int, float32, bool]{})
        f10(S2[int, int, string]{}, S2[int, float32, bool]{})
        f10(S2[P, int, P]{}, S2[P, float32, bool]{})
}

// corner case for type inference
// (was bug: after instanting f11, the type-checker didn't mark f11 as non-generic)

func f11[T any]()

func _() {
	f11[int]()
}

// the previous example was extracted from

func f12[T interface{m() T}]()

type A[T any] T

func (a A[T]) m() A[T]

func _[T any]() {
	f12[A[T]]()
}

// method expressions

func (_ S1[P]) m()

func _() {
	m := S1[int].m
	m(struct { f int }{42})
}

func _[T any] (x T) {
        m := S1[T].m
        m(S1[T]{x})
}

// type parameters in methods (generalization)

type R0 struct{}

func (R0) _[ /* ERROR methods cannot have type parameters */ T any](x T)
func (R0 /* ERROR invalid receiver */ ) _[ /* ERROR methods cannot have type parameters */ R0 any]() // scope of type parameters starts at "func"

type R1[A, B any] struct{}

func (_ R1[A, B]) m0(A, B)
func (_ R1[A, B]) m1[ /* ERROR methods cannot have type parameters */ T any](A, B, T) T
func (_ R1 /* ERROR not a generic type */ [R1, _]) _()
func (_ R1[A, B]) _[ /* ERROR methods cannot have type parameters */ A /* ERROR redeclared */ any](B)

func _() {
        var r R1[int, string]
        r.m1[rune](42, "foo", 'a')
        r.m1[rune](42, "foo", 1.2 /* ERROR cannot use .* as rune .* \(truncated\) */)
        r.m1(42, "foo", 1.2) // using type inference
        var _ float64 = r.m1(42, "foo", 1.2)
}

type I1[A any] interface {
        m1(A)
}

var _ I1[int] = r1[int]{}

type r1[T any] struct{}

func (_ r1[T]) m1(T)

type I2[A, B any] interface {
        m1(A)
        m2(A) B
}

var _ I2[int, float32] = R2[int, float32]{}

type R2[P, Q any] struct{}

func (_ R2[X, Y]) m1(X)
func (_ R2[X, Y]) m2(X) Y

// type assertions and type switches over generic types
// NOTE: These are currently disabled because it's unclear what the correct
// approach is, and one can always work around by assigning the variable to
// an interface first.

// // ReadByte1 corresponds to the ReadByte example in the draft design.
// func ReadByte1[T io.Reader](r T) (byte, error) {
// 	if br, ok := r.(io.ByteReader); ok {
// 		return br.ReadByte()
// 	}
// 	var b [1]byte
// 	_, err := r.Read(b[:])
// 	return b[0], err
// }
//
// // ReadBytes2 is like ReadByte1 but uses a type switch instead.
// func ReadByte2[T io.Reader](r T) (byte, error) {
//         switch br := r.(type) {
//         case io.ByteReader:
//                 return br.ReadByte()
//         }
// 	var b [1]byte
// 	_, err := r.Read(b[:])
// 	return b[0], err
// }
//
// // type assertions and type switches over generic types are strict
// type I3 interface {
//         m(int)
// }
//
// type I4 interface {
//         m() int // different signature from I3.m
// }
//
// func _[T I3](x I3, p T) {
//         // type assertions and type switches over interfaces are not strict
//         _ = x.(I4)
//         switch x.(type) {
//         case I4:
//         }
// 
//         // type assertions and type switches over generic types are strict
//         _ = p /* ERROR cannot have dynamic type I4 */.(I4)
//         switch p.(type) {
//         case I4 /* ERROR cannot have dynamic type I4 */ :
//         }
// }

// type assertions and type switches over generic types lead to errors for now

func _[T any](x T) {
	_ = x /* ERROR not an interface */ .(int)
	switch x /* ERROR not an interface */ .(type) {
	}

	// work-around
	var t interface{} = x
	_ = t.(int)
	switch t.(type) {
	}
}

func _[T interface{type int}](x T) {
	_ = x /* ERROR not an interface */ .(int)
	switch x /* ERROR not an interface */ .(type) {
	}

	// work-around
	var t interface{} = x
	_ = t.(int)
	switch t.(type) {
	}
}

// error messages related to type bounds mention those bounds
type C[P any] interface{}

func _[P C[P]] (x P) {
	x.m /* ERROR x.m undefined */ ()
}

type I interface {}

func _[P I] (x P) {
	x.m /* ERROR interface I has no method m */ ()
}

func _[P interface{}] (x P) {
	x.m /* ERROR type bound for P has no method m */ ()
}

func _[P any] (x P) {
	x.m /* ERROR type bound for P has no method m */ ()
}