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author | Ian Lance Taylor <iant@golang.org> | 2021-07-14 14:46:09 -0700 |
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committer | Ian Lance Taylor <iant@golang.org> | 2021-07-21 19:25:48 +0000 |
commit | 48c88f1b1bac1ef4fc81246a7f31933f8f922706 (patch) | |
tree | fbab30fe4bdc1734cfc86377510be3d50e04e01e | |
parent | 9e26569293c13974d210fd588ebfd29b857d8525 (diff) | |
download | go-48c88f1b1bac1ef4fc81246a7f31933f8f922706.tar.gz go-48c88f1b1bac1ef4fc81246a7f31933f8f922706.zip |
reflect: add Value.CanConvert
For #395
For #46746
Change-Id: I4bfc094cf1cecd27ce48e31f92384cf470f371a6
Reviewed-on: https://go-review.googlesource.com/c/go/+/334669
Trust: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>
Reviewed-by: Joe Tsai <thebrokentoaster@gmail.com>
-rw-r--r-- | api/go1.17.txt | 1 | ||||
-rw-r--r-- | doc/go1.17.html | 12 | ||||
-rw-r--r-- | src/reflect/all_test.go | 9 | ||||
-rw-r--r-- | src/reflect/value.go | 20 |
4 files changed, 42 insertions, 0 deletions
diff --git a/api/go1.17.txt b/api/go1.17.txt index 3d0a464fec..48505381f1 100644 --- a/api/go1.17.txt +++ b/api/go1.17.txt @@ -80,6 +80,7 @@ pkg net/url, method (Values) Has(string) bool pkg reflect, func VisibleFields(Type) []StructField pkg reflect, method (Method) IsExported() bool pkg reflect, method (StructField) IsExported() bool +pkg reflect, method (Value) CanConvert(Type) bool pkg runtime/cgo (darwin-amd64-cgo), func NewHandle(interface{}) Handle pkg runtime/cgo (darwin-amd64-cgo), method (Handle) Delete() pkg runtime/cgo (darwin-amd64-cgo), method (Handle) Value() interface{} diff --git a/doc/go1.17.html b/doc/go1.17.html index b31006fe65..7739d1c62e 100644 --- a/doc/go1.17.html +++ b/doc/go1.17.html @@ -989,6 +989,18 @@ func Foo() bool { <dl id="reflect"><dt><a href="/pkg/reflect/">reflect</a></dt> <dd> + <p><!-- CL 334669 --> + The new + <a href="/pkg/reflect/#Value.CanConvert"><code>Value.CanConvert</code></a> + method reports whether a value can be converted to a type. + This may be used to avoid a panic when converting a slice to an + array pointer type if the slice is too short. + Previously it was sufficient to use + <a href="/pkg/reflect/#Type.ConvertibleTo"><code>Type.ConvertibleTo</code></a> + for this, but the newly permitted conversion from slice to array + pointer type can panic even if the types are convertible. + </p> + <p><!-- CL 266197 --> The new <a href="/pkg/reflect/#StructField.IsExported"><code>StructField.IsExported</code></a> diff --git a/src/reflect/all_test.go b/src/reflect/all_test.go index 0db5e13217..eac27e886f 100644 --- a/src/reflect/all_test.go +++ b/src/reflect/all_test.go @@ -4304,6 +4304,9 @@ func TestConvert(t *testing.T) { // vout1 represents the in value converted to the in type. v1 := tt.in + if !v1.CanConvert(t1) { + t.Errorf("ValueOf(%T(%[1]v)).CanConvert(%s) = false, want true", tt.in.Interface(), t1) + } vout1 := v1.Convert(t1) out1 := vout1.Interface() if vout1.Type() != tt.in.Type() || !DeepEqual(out1, tt.in.Interface()) { @@ -4311,6 +4314,9 @@ func TestConvert(t *testing.T) { } // vout2 represents the in value converted to the out type. + if !v1.CanConvert(t2) { + t.Errorf("ValueOf(%T(%[1]v)).CanConvert(%s) = false, want true", tt.in.Interface(), t2) + } vout2 := v1.Convert(t2) out2 := vout2.Interface() if vout2.Type() != tt.out.Type() || !DeepEqual(out2, tt.out.Interface()) { @@ -4371,6 +4377,9 @@ func TestConvertPanic(t *testing.T) { if !v.Type().ConvertibleTo(pt) { t.Errorf("[]byte should be convertible to *[8]byte") } + if v.CanConvert(pt) { + t.Errorf("slice with length 4 should not be convertible to *[8]byte") + } shouldPanic("reflect: cannot convert slice with length 4 to pointer to array with length 8", func() { _ = v.Convert(pt) }) diff --git a/src/reflect/value.go b/src/reflect/value.go index 9dce251ac5..6f878eba5b 100644 --- a/src/reflect/value.go +++ b/src/reflect/value.go @@ -2811,6 +2811,26 @@ func (v Value) Convert(t Type) Value { return op(v, t) } +// CanConvert reports whether the value v can be converted to type t. +// If v.CanConvert(t) returns true then v.Convert(t) will not panic. +func (v Value) CanConvert(t Type) bool { + vt := v.Type() + if !vt.ConvertibleTo(t) { + return false + } + // Currently the only conversion that is OK in terms of type + // but that can panic depending on the value is converting + // from slice to pointer-to-array. + if vt.Kind() == Slice && t.Kind() == Ptr && t.Elem().Kind() == Array { + n := t.Elem().Len() + h := (*unsafeheader.Slice)(v.ptr) + if n > h.Len { + return false + } + } + return true +} + // convertOp returns the function to convert a value of type src // to a value of type dst. If the conversion is illegal, convertOp returns nil. func convertOp(dst, src *rtype) func(Value, Type) Value { |