constraints: remove Slice/Map/Chan

Now that we permit arbitrary types as constraints, we no longer need them.

For #48424

Change-Id: I15fef26a563988074650cb0801895b002c44148a
Reviewed-on: https://go-review.googlesource.com/c/go/+/359258
Trust: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>

2 files changed, 12 insertions, 65 deletions

diff --git a/src/constraints/constraints.go b/src/constraints/constraints.go
index 2a5f673a7e..2c033dff47 100644
--- a/src/constraints/constraints.go
+++ b/src/constraints/constraints.go
@@ -48,18 +48,3 @@ type Complex interface {
 type Ordered interface {
 	Integer | Float | ~string
 }
-
-// Slice is a constraint that matches slices of any element type.
-type Slice[Elem any] interface {
-	~[]Elem
-}
-
-// Map is a constraint that matches maps of any element and value type.
-type Map[Key comparable, Val any] interface {
-	~map[Key]Val
-}
-
-// Chan is a constraint that matches channels of any element type.
-type Chan[Elem any] interface {
-	~chan Elem
-}
diff --git a/src/constraints/constraints_test.go b/src/constraints/constraints_test.go
index db5a957313..538dc843cc 100644
--- a/src/constraints/constraints_test.go
+++ b/src/constraints/constraints_test.go
@@ -15,15 +15,12 @@ import (
 )
 
 type (
-	testSigned[T Signed]                      struct{ f T }
-	testUnsigned[T Unsigned]                  struct{ f T }
-	testInteger[T Integer]                    struct{ f T }
-	testFloat[T Float]                        struct{ f T }
-	testComplex[T Complex]                    struct{ f T }
-	testOrdered[T Ordered]                    struct{ f T }
-	testSlice[T Slice[E], E any]              struct{ f T }
-	testMap[T Map[K, V], K comparable, V any] struct{ f T }
-	testChan[T Chan[E], E any]                struct{ f T }
+	testSigned[T Signed]     struct{ f T }
+	testUnsigned[T Unsigned] struct{ f T }
+	testInteger[T Integer]   struct{ f T }
+	testFloat[T Float]       struct{ f T }
+	testComplex[T Complex]   struct{ f T }
+	testOrdered[T Ordered]   struct{ f T }
 )
 
 // TestTypes passes if it compiles.
@@ -40,35 +37,6 @@ type TestTypes struct {
 	_ testOrdered[int]
 	_ testOrdered[float64]
 	_ testOrdered[string]
-	_ testSlice[[]int, int]
-	_ testMap[map[int]bool, int, bool]
-	_ testChan[chan int, int]
-}
-
-func infer1[S Slice[E], E any](s S, v E) S                     { return s }
-func infer2[M Map[K, V], K comparable, V any](m M, k K, v V) M { return m }
-func infer3[C Chan[E], E any](c C, v E) C                      { return c }
-
-func TestInference(t *testing.T) {
-	var empty interface{}
-
-	type S []int
-	empty = infer1(S{}, 0)
-	if _, ok := empty.(S); !ok {
-		t.Errorf("infer1(S) returned %T, expected S", empty)
-	}
-
-	type M map[int]bool
-	empty = infer2(M{}, 0, false)
-	if _, ok := empty.(M); !ok {
-		t.Errorf("infer2(M) returned %T, expected M", empty)
-	}
-
-	type C chan bool
-	empty = infer3(make(C), true)
-	if _, ok := empty.(C); !ok {
-		t.Errorf("infer3(C) returned %T, expected C", empty)
-	}
 }
 
 var prolog = []byte(`
@@ -77,15 +45,12 @@ package constrainttest
 import "constraints"
 
 type (
-	testSigned[T constraints.Signed]                      struct{ f T }
-	testUnsigned[T constraints.Unsigned]                  struct{ f T }
-	testInteger[T constraints.Integer]                    struct{ f T }
-	testFloat[T constraints.Float]                        struct{ f T }
-	testComplex[T constraints.Complex]                    struct{ f T }
-	testOrdered[T constraints.Ordered]                    struct{ f T }
-	testSlice[T constraints.Slice[E], E any]              struct{ f T }
-	testMap[T constraints.Map[K, V], K comparable, V any] struct{ f T }
-	testChan[T constraints.Chan[E], E any]                struct{ f T }
+	testSigned[T constraints.Signed]     struct{ f T }
+	testUnsigned[T constraints.Unsigned] struct{ f T }
+	testInteger[T constraints.Integer]   struct{ f T }
+	testFloat[T constraints.Float]       struct{ f T }
+	testComplex[T constraints.Complex]   struct{ f T }
+	testOrdered[T constraints.Ordered]   struct{ f T }
 )
 `)
 
@@ -115,9 +80,6 @@ func TestFailure(t *testing.T) {
 		{"testFloat", "int8"},
 		{"testComplex", "float64"},
 		{"testOrdered", "bool"},
-		{"testSlice", "int, int"},
-		{"testMap", "string, string, string"},
-		{"testChan", "[]int, int"},
 	} {
 		i := i
 		test := test