This CL makes reflect require that values be assignable to the target type
in exactly the same places where that is the rule in Go. It also adds
the Implements and AssignableTo methods so that callers can check
the types themselves so as to avoid a panic.
Before this CL, reflect required strict type identity.
This CL expands Call to accept and correctly marshal arbitrary
argument lists for variadic functions; it introduces CallSlice for use
in the case where the slice for the variadic argument is already known.
Fixes#327.
Fixes#1212.
R=r, dsymonds
CC=golang-dev
https://golang.org/cl/4439058
* Reduces malloc counts during gob encoder/decoder test from 6/6 to 3/5.
The current reflect uses Set to mean two subtly different things.
(1) If you have a reflect.Value v, it might just represent
itself (as in v = reflect.NewValue(42)), in which case calling
v.Set only changed v, not any other data in the program.
(2) If you have a reflect Value v derived from a pointer
or a slice (as in x := []int{42}; v = reflect.NewValue(x).Index(0)),
v represents the value held there. Changing x[0] affects the
value returned by v.Int(), and calling v.Set affects x[0].
This was not really by design; it just happened that way.
The motivation for the new reflect implementation was
to remove mallocs. The use case (1) has an implicit malloc
inside it. If you can do:
v := reflect.NewValue(0)
v.Set(42)
i := v.Int() // i = 42
then that implies that v is referring to some underlying
chunk of memory in order to remember the 42; that is,
NewValue must have allocated some memory.
Almost all the time you are using reflect the goal is to
inspect or to change other data, not to manipulate data
stored solely inside a reflect.Value.
This CL removes use case (1), so that an assignable
reflect.Value must always refer to some other piece of data
in the program. Put another way, removing this case would
make
v := reflect.NewValue(0)
v.Set(42)
as illegal as
0 = 42.
It would also make this illegal:
x := 0
v := reflect.NewValue(x)
v.Set(42)
for the same reason. (Note that right now, v.Set(42) "succeeds"
but does not change the value of x.)
If you really wanted to make v refer to x, you'd start with &x
and dereference it:
x := 0
v := reflect.NewValue(&x).Elem() // v = *&x
v.Set(42)
It's pretty rare, except in tests, to want to use NewValue and then
call Set to change the Value itself instead of some other piece of
data in the program. I haven't seen it happen once yet while
making the tree build with this change.
For the same reasons, reflect.Zero (formerly reflect.MakeZero)
would also return an unassignable, unaddressable value.
This invalidates the (awkward) idiom:
pv := ... some Ptr Value we have ...
v := reflect.Zero(pv.Type().Elem())
pv.PointTo(v)
which, when the API changed, turned into:
pv := ... some Ptr Value we have ...
v := reflect.Zero(pv.Type().Elem())
pv.Set(v.Addr())
In both, it is far from clear what the code is trying to do. Now that
it is possible, this CL adds reflect.New(Type) Value that does the
obvious thing (same as Go's new), so this code would be replaced by:
pv := ... some Ptr Value we have ...
pv.Set(reflect.New(pv.Type().Elem()))
The changes just described can be confusing to think about,
but I believe it is because the old API was confusing - it was
conflating two different kinds of Values - and that the new API
by itself is pretty simple: you can only Set (or call Addr on)
a Value if it actually addresses some real piece of data; that is,
only if it is the result of dereferencing a Ptr or indexing a Slice.
If you really want the old behavior, you'd get it by translating:
v := reflect.NewValue(x)
into
v := reflect.New(reflect.Typeof(x)).Elem()
v.Set(reflect.NewValue(x))
Gofix will not be able to help with this, because whether
and how to change the code depends on whether the original
code meant use (1) or use (2), so the developer has to read
and think about the code.
You can see the effect on packages in the tree in
https://golang.org/cl/4423043/.
R=r
CC=golang-dev
https://golang.org/cl/4435042
Type is now an interface that implements all the possible type methods.
Instead of a type switch on a reflect.Type t, switch on t.Kind().
If a method is invoked on the wrong kind of type (for example,
calling t.Field(0) when t.Kind() != Struct), the call panics.
There is one method renaming: t.(*ChanType).Dir() is now t.ChanDir().
Value is now a struct value that implements all the possible value methods.
Instead of a type switch on a reflect.Value v, switch on v.Kind().
If a method is invoked on the wrong kind of value (for example,
calling t.Recv() when t.Kind() != Chan), the call panics.
Since Value is now a struct, not an interface, its zero value
cannot be compared to nil. Instead of v != nil, use v.IsValid().
Instead of other uses of nil as a Value, use Value{}, the zero value.
Many methods have been renamed, most due to signature conflicts:
OLD NEW
v.(*ArrayValue).Elem v.Index
v.(*BoolValue).Get v.Bool
v.(*BoolValue).Set v.SetBool
v.(*ChanType).Dir v.ChanDir
v.(*ChanValue).Get v.Pointer
v.(*ComplexValue).Get v.Complex
v.(*ComplexValue).Overflow v.OverflowComplex
v.(*ComplexValue).Set v.SetComplex
v.(*FloatValue).Get v.Float
v.(*FloatValue).Overflow v.OverflowFloat
v.(*FloatValue).Set v.SetFloat
v.(*FuncValue).Get v.Pointer
v.(*InterfaceValue).Get v.InterfaceData
v.(*IntValue).Get v.Int
v.(*IntValue).Overflow v.OverflowInt
v.(*IntValue).Set v.SetInt
v.(*MapValue).Elem v.MapIndex
v.(*MapValue).Get v.Pointer
v.(*MapValue).Keys v.MapKeys
v.(*MapValue).SetElem v.SetMapIndex
v.(*PtrValue).Get v.Pointer
v.(*SliceValue).Elem v.Index
v.(*SliceValue).Get v.Pointer
v.(*StringValue).Get v.String
v.(*StringValue).Set v.SetString
v.(*UintValue).Get v.Uint
v.(*UintValue).Overflow v.OverflowUint
v.(*UintValue).Set v.SetUint
v.(*UnsafePointerValue).Get v.Pointer
v.(*UnsafePointerValue).Set v.SetPointer
Part of the motivation for this change is to enable a more
efficient implementation of Value, one that does not allocate
memory during most operations. To reduce the size of the CL,
this CL's implementation is a wrapper around the old API.
Later CLs will make the implementation more efficient without
changing the API.
Other CLs to be submitted at the same time as this one
add support for this change to gofix (4343047) and update
the Go source tree (4353043).
R=gri, iant, niemeyer, r, rog, gustavo, r2
CC=golang-dev
https://golang.org/cl/4281055
This change makes it possible to take the address of a
struct field or slice element in order to call a method that
requires a pointer receiver.
Existing code that uses the Value.Addr method will have
to change (as gob does in this CL) to call UnsafeAddr instead.
R=r, rog
CC=golang-dev
https://golang.org/cl/4239052
I have written a tool to verify Printf calls, and although it's not
ready to be reviewed yet it's already uncovered a spate of problems
in the repository. I'm sending this CL to break the changes into
pieces; as the tool improves it will find more, I'm sure.
R=rsc
CC=golang-dev
https://golang.org/cl/3427043
(Argument: For any *PtrValue p, it should
always be possible to do: p.PointTo(p.Elem()),
even if p.Elem() is nil.)
Fixes#1028.
R=rsc
CC=golang-dev, r
https://golang.org/cl/1938044
parsing and printing to new syntax.
Use -oldparser to parse the old syntax,
use -oldprinter to print the old syntax.
2) Change default gofmt formatting settings
to use tabs for indentation only and to use
spaces for alignment. This will make the code
alignment insensitive to an editor's tabwidth.
Use -spaces=false to use tabs for alignment.
3) Manually changed src/exp/parser/parser_test.go
so that it doesn't try to parse the parser's
source files using the old syntax (they have
new syntax now).
4) gofmt -w src misc test/bench
4th set of files.
R=rsc
CC=golang-dev
https://golang.org/cl/180049
- enabled for function declarations (not just function literals)
- applied gofmt -w $GOROOT/src
(look for instance at src/pkg/debug/elf/elf.go)
R=r, rsc
CC=go-dev
http://go/go-review/1026006
whole-package compilation. new Makefiles,
tests now in separate package
bytes
flag
fmt
io
math
once
os
reflect
strconv
sync
time
utf8
delete import "xxx" in package xxx.
inside package xxx, xxx is not declared
anymore so s/xxx.//g
delete file and package level forward declarations.
note the new internal_test.go and sync
and strconv to provide public access to
internals during testing. the installed version
of the package omits that file and thus does
not open the internals to all clients.
R=r
OCL=33065
CL=33097
