I'd suggest simply
func (b *Binlog) writeArgumentToOutput(writer writer, arg uint64) error {
/* do the writing */ }
and doing the actual conversions at the call-site. It's type-safe, shorter,
faster and more idiomatic - with the tiny downside of a `uint64()` here and
there.
Alternatively, use reflect as it's intended to - something like
func writeArgumentToOutput(writer writer, arg interface{}) error {
rv := reflect.ValueOf(arg)
var v uint64
if k := rv.Kind(); k >= reflect.Int && k < reflect.Uint {
v = uint64(rv.Int())
} else if k <= reflect.Uintptr {
v = rv.Uint()
} else {
return fmt.Errorf("Unsupported type: %T\n", reflect.TypeOf(arg))
}
/* write v */
return nil
}
this is probably a bit slower than the above, type-safe version, but
probably not noticeably slower than the unsafe large type-switch above and
has the benefit of also not needing conversion at the call-site (it also
works correctly with all integer types, which the type-switch doesn't).
But in the end, any slowness here comes from passing things as an
interface{}, instead of just as a value. You can't really optimize that
away, because it's inherent in the approach.
On Sun, Nov 25, 2018 at 5:32 PM Michel Levieux <m.levi...@capitaldata.fr>
wrote:
> No offense intended, but that code is wrong on so many levels...
>
>
> I strongly believe you that you are not trying to offend anyone, but this
> question is interesting for me too, and I'd like more details. Could you
> please explain, from worst to "less worst", what's wrong with this code?
> Reflection is sometimes really misleading for people who don't have a deep
> understanding of the compiler, and such pieces of code exist all around the
> internet. Would you give us a more precise feedback?
>
> Thanks in advance!
>
> Le dim. 25 nov. 2018 à 17:17, Jan Mercl <0xj...@gmail.com> a écrit :
>
>> No offense intended, but that code is wrong on so many levels...
>>
>> On Sun, Nov 25, 2018, 17:10 <lary...@gmail.com> wrote:
>>
>>> The code below consumes ~40% of the total execution time. According to
>>> the profiler i := uint64(arg.(uint32)) is a major contributor
>>>
>>> // Cast the integer argument to uint64 and call a "writer"
>>> // The "writer" knows how many bytes to add to the binary stream
>>> // Type casts from interface{} to integer consume 40% of the overall
>>> // time. Can I do better? What is interface{} in Golang?
>>> func (b *Binlog) writeArgumentToOutput(writer writer, arg interface{},
>>> argKind reflect.Kind) error {
>>> // unsafe pointer to the data depends on the data type
>>> var err error
>>> switch argKind {
>>> case reflect.Int8:
>>> i := uint64(arg.(int8))
>>> err = writer.write(b.ioWriter, unsafe.Pointer(&i))
>>> case reflect.Int16:
>>> i := uint64(arg.(int16))
>>> err = writer.write(b.ioWriter, unsafe.Pointer(&i))
>>> case reflect.Int32:
>>> i := uint64(arg.(int32))
>>> err = writer.write(b.ioWriter, unsafe.Pointer(&i))
>>> case reflect.Int64:
>>> i := uint64(arg.(int64))
>>> err = writer.write(b.ioWriter, unsafe.Pointer(&i))
>>> case reflect.Uint8:
>>> i := uint64(arg.(uint8))
>>> err = writer.write(b.ioWriter, unsafe.Pointer(&i))
>>> case reflect.Uint16:
>>> i := uint64(arg.(uint16))
>>> err = writer.write(b.ioWriter, unsafe.Pointer(&i))
>>> case reflect.Uint32:
>>> i := uint64(arg.(uint32))
>>> err = writer.write(b.ioWriter, unsafe.Pointer(&i))
>>> case reflect.Uint64:
>>> i := uint64(arg.(uint64))
>>> err = writer.write(b.ioWriter, unsafe.Pointer(&i))
>>> case reflect.Int:
>>> i := uint64(arg.(int))
>>> err = writer.write(b.ioWriter, unsafe.Pointer(&i))
>>> case reflect.Uint:
>>> i := uint64(arg.(uint))
>>> err = writer.write(b.ioWriter, unsafe.Pointer(&i))
>>> default:
>>> return fmt.Errorf("Unsupported type: %T\n", reflect.TypeOf(arg))
>>> }
>>> return err
>>> }
>>>
>>>
>>> --
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>> --
>>
>> -j
>>
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