cmd/compile/internal/types2: implement generic slice expressions

For now, the constraint's underlying type set must be a single type that is sliceable. Change-Id: I08b6a2e88fe35e8238a95b3f40dc969689021a0f Reviewed-on: https://go-review.googlesource.com/c/go/+/354070 Trust: Robert Griesemer <[email protected]> Run-TryBot: Robert Griesemer <[email protected]> TryBot-Result: Go Bot <[email protected]> Reviewed-by: Ian Lance Taylor <[email protected]>
cloudflare · Oct 5, 2021 · 7e69c5d · 7e69c5d
1 parent 097a82f
commit 7e69c5d
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Showing 2 changed files with 7 additions and 8 deletions.
diff --git a/src/cmd/compile/internal/types2/index.go b/src/cmd/compile/internal/types2/index.go
@@ -207,7 +207,7 @@ func (check *Checker) sliceExpr(x *operand, e *syntax.SliceExpr) {
 
  valid := false
  length := int64(-1) // valid if >= 0
- switch typ := under(x.typ).(type) {
+ switch typ := optype(x.typ).(type) {
  case *Basic:
  if isString(typ) {
  if e.Full {
@@ -246,11 +246,6 @@ func (check *Checker) sliceExpr(x *operand, e *syntax.SliceExpr) {
  case *Slice:
  valid = true
  // x.typ doesn't change
-
- case *TypeParam:
- check.error(x, "generic slice expressions not yet implemented")
- x.mode = invalid
- return
  }
 
  if !valid {

diff --git a/src/cmd/compile/internal/types2/testdata/check/typeparams.go2 b/src/cmd/compile/internal/types2/testdata/check/typeparams.go2
@@ -115,9 +115,13 @@ func _[T interface{ [10]byte | string }](x T, i int) { _ = x[i]; _ = x[9]; _ = x
 func _[T interface{ [10]int | *[20]int | []int }](x T, i int) { _ = x[i]; _ = x[9]; _ = x[10 /* ERROR out of bounds */ ] }
 
 // slicing
-// TODO(gri) implement this
 
-func _[T interface{ ~string }] (x T, i, j, k int) { _ = x /* ERROR generic slice expressions not yet implemented */ [i:j:k] }
+func _[T interface{ ~[10]E }, E any] (x T, i, j, k int) { var _ []E = x[i:j] }
+func _[T interface{ ~[10]E }, E any] (x T, i, j, k int) { var _ []E = x[i:j:k] }
+func _[T interface{ ~[]byte }] (x T, i, j, k int) { var _ T = x[i:j] }
+func _[T interface{ ~[]byte }] (x T, i, j, k int) { var _ T = x[i:j:k] }
+func _[T interface{ ~string }] (x T, i, j, k int) { var _ T = x[i:j] }
+func _[T interface{ ~string }] (x T, i, j, k int) { var _ T = x /* ERROR 3-index slice of string */ [i:j:k] }
 
 // len/cap built-ins