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Implement Value.TypeOf() #104

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b09d1cb
Implement Value.TypeOf()
stroiman May 20, 2025
c420dad
Remove unnecessary null check
stroiman May 21, 2025
0ee6942
Use consistent C-style
stroiman May 21, 2025
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4 changes: 4 additions & 0 deletions CHANGELOG.md
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Expand Up @@ -6,6 +6,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0

## [Unreleased]

### Added

- Add support for `Value.TypeOf()` corresponding to JavaScript `typeof` operator.

### Changed

## [v0.33.0] - 2025-05-15
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7 changes: 7 additions & 0 deletions errors.cc
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@@ -1,3 +1,4 @@
#include <stdlib.h>
#include <sstream>

#include "deps/include/v8-exception.h"
Expand Down Expand Up @@ -48,3 +49,9 @@ RtnError ExceptionError(TryCatch& try_catch, Isolate* iso, Local<Context> ctx) {

return rtn;
}

void ErrorRelease(RtnError err) {
free((void*)err.msg);
free((void*)err.location);
free((void*)err.stack);
}
2 changes: 2 additions & 0 deletions errors.h
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Expand Up @@ -43,6 +43,8 @@ typedef struct {
RtnError error;
} RtnValue;

void ErrorRelease(RtnError err);

#ifdef __cplusplus
}
#endif
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42 changes: 34 additions & 8 deletions value.cc
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@@ -1,8 +1,10 @@
#include "value.h"
#include <stdlib.h>
#include "context.h"
#include "deps/include/v8-context.h"
#include "deps/include/v8-exception.h"
#include "errors.h"
#include "isolate-macros.h"
#include "utils.h"
#include "value-macros.h"

#define ISOLATE_SCOPE_INTERNAL_CONTEXT(iso) \
Expand All @@ -11,6 +13,29 @@

using namespace v8;

RtnString StringToRtnString(v8::Isolate* iso, Local<String> val) {
RtnString res = {};
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I don't think the {} initialization does anything (the original code had {0} with no purpose there).

RtnString and RtnError should have constructors (or default initializers) to ensure values are cleared.

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{} zeros the fields. But I don't know the difference between that and {0}.

However, these two types RtnString and RtnError are exposed to Go code, i.e. Go code actually looks up the field - so I don't think you can add constructors? Because then it would be a C++ type, not a C type?

You could make them "anonymous" (don't know the correct term), like m_ctx where Go code just has pointer values it can pass back to C functions - and then add functions to look up values, but that also seems somewhat cumbersome.

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As long as you don't add a vtable, it's just compile-time syntactic sugar for running a function every time a value is created.

Relying on a destructor might be dangerous, since the cgo code wouldn't run it.

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I'm not sure I what you mean. But this works - but it generates warnings.

struct RtnError {
  const char* msg;
  const char* location;
  const char* stack;
#ifdef __cplusplus
  RtnError() : msg(0), location(0), stack(0) {};
#endif
};

To get "methods" on the type, I changed from typedef struct { ... } RtnError to struct RtnError { }.

This caused compilation errors, both in .h and .go files.

  • In .h files, extern RtnValue SomeFunction(...); had to be changed to extern struct RtnValue SomeFunction(...)
  • In .go files, C.RtnValue had to be changed to C.struct_RtnValue.

I could avoid those changes by adding typedef struct RtnError RtnError; though I probably shouldn't use the same identifier?

The warnings are:

./context.h:80:17: warning: 'RunScript' has C-linkage specified, but returns user-defined type 'RtnValue' which is incompatible with C [-Wreturn-type-c-linkage]

But if I remove the initializer from some function creating a RtnError, all tests are still passing, and if I then remove the constructor, it fails at runtime.

But I had the impression from your comments that there is a simpler way?

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@tommie tommie May 22, 2025 •
edited
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Oh, I see, this needs to compile in C mode. Of course it does. My bad.

Ok, helper function it is...

Edit The helper function was about another comment... (Does it show there's too much going on for me to keep track. ;)

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But here: still need to add back the zero into the intializer to make it do something. https://stackoverflow.com/a/10828333

res.length = val->Utf8LengthV2(iso);
res.data = (char*)(malloc(res.length));
val->WriteUtf8V2(iso, (char*)res.data, res.length);
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I suggest sticking to either C- or C++-style casts in one function. :)

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I agree :)

return res;
}

RtnString ExceptionToRtnString(TryCatch& try_catch,
v8::Isolate* iso,
Local<Context> ctx) {
RtnString res = {};
res.error = ExceptionError(try_catch, iso, ctx);
return res;
}

void RtnStringRelease(RtnString rtnString) {
if (rtnString.data) {
free((void*)rtnString.data);
}
ErrorRelease(rtnString.error);
}

void ValueRelease(ValuePtr ptr) {
if (ptr == nullptr) {
return;
Expand Down Expand Up @@ -223,16 +248,11 @@ double ValueToNumber(ValuePtr ptr) {

RtnString ValueToDetailString(ValuePtr ptr) {
LOCAL_VALUE(ptr);
RtnString rtn = {0};
Local<String> str;
if (!value->ToDetailString(local_ctx).ToLocal(&str)) {
rtn.error = ExceptionError(try_catch, iso, local_ctx);
return rtn;
return ExceptionToRtnString(try_catch, iso, local_ctx);
}
String::Utf8Value ds(iso, str);
rtn.data = CopyString(ds);
rtn.length = ds.length();
return rtn;
return StringToRtnString(iso, str);
}

RtnString ValueToString(ValuePtr ptr) {
Expand Down Expand Up @@ -565,3 +585,9 @@ int ValueIsModuleNamespaceObject(ValuePtr ptr) {
LOCAL_VALUE(ptr);
return value->IsModuleNamespaceObject();
}

RtnString ValueTypeOf(ValuePtr ptr) {
LOCAL_VALUE(ptr);
Local<String> result = value->TypeOf(iso);
return StringToRtnString(iso, result);
}
10 changes: 8 additions & 2 deletions value.go
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Expand Up @@ -240,8 +240,8 @@ func (v *Value) Object() *Object {
// are returned as-is, objects will return `[object Object]` and functions will
// print their definition.
func (v *Value) String() string {
s := C.ValueToString(v.ptr)
defer C.free(unsafe.Pointer(s.data))
var s C.RtnString = C.ValueToString(v.ptr)
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Normally := is preferred. Why this change?

defer C.RtnStringRelease(s)
return C.GoStringN(s.data, C.int(s.length))
}

Expand Down Expand Up @@ -614,3 +614,9 @@ func (v *Value) SharedArrayBufferGetContents() ([]byte, func(), error) {

return byte_slice, release, nil
}

func (v *Value) TypeOf() string {
var s C.RtnString = C.ValueTypeOf(v.ptr)
defer C.RtnStringRelease(s)
return C.GoStringN(s.data, C.int(s.length))
}
3 changes: 3 additions & 0 deletions value.h
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Expand Up @@ -53,7 +53,9 @@ typedef struct {
} RtnString;

void ValueRelease(ValuePtr ptr);
void RtnStringRelease(RtnString rtnString);
extern RtnString ValueToString(ValuePtr ptr);
extern RtnString ValueTypeOf(ValuePtr ptr);
const uint32_t* ValueToArrayIndex(ValuePtr ptr);
int ValueToBoolean(ValuePtr ptr);
int32_t ValueToInt32(ValuePtr ptr);
Expand Down Expand Up @@ -163,5 +165,6 @@ extern BackingStorePtr SharedArrayBufferGetBackingStore(ValuePtr ptr);

#ifdef __cplusplus
}

#endif
#endif
28 changes: 28 additions & 0 deletions value_test.go
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Expand Up @@ -817,3 +817,31 @@ func TestValueArrayBufferContents(t *testing.T) {
t.Fatalf("Expected an error trying call SharedArrayBufferGetContents on value of incorrect type")
}
}

func TestValueTypeOf(t *testing.T) {
t.Parallel()
iso := v8.NewIsolate()
defer iso.Dispose()
ctx := v8.NewContext(iso)
defer ctx.Close()

str1, _ := v8.NewValue(iso, "String")
if got := str1.TypeOf(); got != "string" {
t.Errorf(`NewValue("String"): expected string, got %s`, got)
}

str2, _ := ctx.RunScript("'string'", "")
if got := str2.TypeOf(); got != "string" {
t.Errorf("TypeOf('string'): expected string, got %s", got)
}

num1, _ := v8.NewValue(iso, 0.01)
if got := num1.TypeOf(); got != "number" {
t.Errorf(`NewValue(0.01): expected number, got %s`, got)
}

num2, _ := ctx.RunScript("0.01", "")
if got := num2.TypeOf(); got != "number" {
t.Errorf("TypeOf(0.01): expected number, got %s", got)
}
}