reflect: support array pointer in Value.Len() #52411
Description
Hello!
Docs says:
package builtin
// The len built-in function returns the length of v, according to its type:
// ...
// Pointer to array: the number of elements in *v (even if v is nil).
// ...
func len(v Type) intBut reflect doesn't support it:
package reflect
// Len returns v's length.
// It panics if v's Kind is not Array, Chan, Map, Slice, or String.
func (v Value) Len() int {
k := v.kind()
switch k { // <-- No array ptr case!
case Array: /* ... */
case Chan: /* ... */
case Map: /* ... */
case Slice: /* ... */
case String: /* ... */
}
panic(&ValueError{"reflect.Value.Len", v.kind()})
}What version of Go are you using (go version)?
$ go version go version go1.18 darwin/arm64
Does this issue reproduce with the latest release?
Yes
What operating system and processor architecture are you using (go env)?
go env Output
$ go env GO111MODULE="on" GOARCH="arm64" GOBIN="/Users/anthony/golang_workspace/bin" GOCACHE="/Users/anthony/Library/Caches/go-build" GOENV="/Users/anthony/Library/Application Support/go/env" GOEXE="" GOEXPERIMENT="" GOFLAGS="" GOHOSTARCH="arm64" GOHOSTOS="darwin" GOINSECURE="" GOMODCACHE="/Users/anthony/golang_workspace/pkg/mod" GONOPROXY="" GONOSUMDB="" GOOS="darwin" GOPATH="/Users/anthony/golang_workspace" GOPRIVATE="" GOPROXY="https://proxy.golang.org,direct" GOROOT="/usr/local/go" GOSUMDB="sum.golang.org" GOTMPDIR="" GOTOOLDIR="/usr/local/go/pkg/tool/darwin_arm64" GOVCS="" GOVERSION="go1.18" GCCGO="gccgo" AR="ar" CC="clang" CXX="clang++" CGO_ENABLED="1" GOMOD="/dev/null" GOWORK="" CGO_CFLAGS="-g -O2" CGO_CPPFLAGS="" CGO_CXXFLAGS="-g -O2" CGO_FFLAGS="-g -O2" CGO_LDFLAGS="-g -O2" PKG_CONFIG="pkg-config" GOGCCFLAGS="-fPIC -arch arm64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/6t/v80c8sfs5zqf38b2yhzq592h0000gn/T/go-build3171440032=/tmp/go-build -gno-record-gcc-switches -fno-common"
What did you do?
https://go.dev/play/p/8rAZrY3A-yJ
package main
import (
"fmt"
"reflect"
)
func main() {
a := [3]int{1, 2, 3}
fmt.Println(len(a))
fmt.Println(reflect.ValueOf(a).Len())
aPtr := &a
fmt.Println(len(aPtr))
fmt.Println(reflect.ValueOf(aPtr).Len()) // panic!
}What did you expect to see?
3
3
3
3
What did you see instead?
3
3
3
panic: reflect: call of reflect.Value.Len on ptr Value