mirror
/
go
mirror of https://github.com/golang/go.git
1
0
Fork 0
Code Issues Packages Projects Releases Wiki Activity

go/types: better comments for range stmt code 

Change-Id: Id7ccf3f47b5ba9d8edd023675122d5f975b89905
This commit is contained in:
Robert Griesemer 2020-01-15 09:09:25 -08:00
parent 172f10b1e2
commit 2b265905e9
1 changed files with 10 additions and 4 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

14
src/go/types/stmt.go
View File

@ -753,7 +753,7 @@ func (check *Checker) stmt(ctxt stmtContext, s ast.Stmt) {
if x.mode != invalid {
typ := x.typ.Underlying()
// TODO(gri) these tests need to be done also for type parameter channel types
// => move into rangeTypes and return an error message instead
// => move into rangeKeyVal and return an error message instead
if typ, _ := typ.(*Chan); typ != nil {
if typ.dir == SendOnly {
check.softErrorf(x.pos(), "cannot range over send-only channel %s", &x)
@ -764,7 +764,7 @@ func (check *Checker) stmt(ctxt stmtContext, s ast.Stmt) {
// ok to continue
}
}
key, val = rangeTypes(typ, isVarName(s.Key), isVarName(s.Value))
key, val = rangeKeyVal(typ, isVarName(s.Key), isVarName(s.Value))
if key == nil {
check.softErrorf(x.pos(), "cannot range over %s", &x)
// ok to continue
@ -851,6 +851,7 @@ func (check *Checker) stmt(ctxt stmtContext, s ast.Stmt) {
}
}
// isVarName reports whether x is a non-nil, non-blank (_) expression.
func isVarName(x ast.Expr) bool {
if x == nil {
return false
@ -859,7 +860,12 @@ func isVarName(x ast.Expr) bool {
return ident == nil || ident.Name != "_"
}
func rangeTypes(typ Type, wantKey, wantVal bool) (Type, Type) {
// rangeKeyVal returns the key and value type produced by a range clause
// over an expression of type typ; if the range clause is not permitted
// the result is (nil, nil). The wantKey, wantVal flags indicate which of
// the values are actually used - this matters if we range over a generic
// type where not all keys or values are of the same type.
func rangeKeyVal(typ Type, wantKey, wantVal bool) (Type, Type) {
switch typ := typ.(type) {
case *Basic:
if isString(typ) {
@ -882,7 +888,7 @@ func rangeTypes(typ Type, wantKey, wantVal bool) (Type, Type) {
first := true
var key, val Type
if typ.Interface().is(func(t Type) bool {
k, v := rangeTypes(t, true, true)
k, v := rangeKeyVal(t, true, true)
if first {
key, val = k, v
first = false