Generate Append functions by template

[yonidavidson]

This requires a bit more refactoring in the C side in order to get a generic structure for this type of functions.

For example:

func (b *TimestampArrayBuilder) Append(val time.Time) error {
	r := C.array_builder_append_timestamp(b.ptr, C.longlong(val.UnixNano()))
	if r.err != nil {
		return errFromResult(r)
	}
	return nil
}

Go type: time.Time

C.array_builder_append_timestamp

should pass a pointer (and the C function will cast it)
val.UnixNano should be defined as a Mutator function for the template.

[tebeka]

@yonidavidson Can you format the code above?

[tebeka]

C.array_builder_append_timestamp should pass a pointer
I don't understand why

[yonidavidson]

C.array_builder_append_timestamp should pass a pointer
I don't understand why

In

func (b *Float64ArrayBuilder) Append(val float64) error {
	r := C.array_builder_append_float(b.ptr, C.double(val))
	if r.err != nil {
		return errFromResult(r)
	}
	return nil
}

we are sending a C.double(val)
in

func (b *Integer64ArrayBuilder) Append(val int64) error {
   r := C.array_builder_append_int(b.ptr, C.longlong(val))
   if r.err != nil {
   	return errFromResult(r)
   }
   return nil
}

we are sending a C.longlong(val)
I think that that the knowledge about C.TYPE should be set by the C layer (we call a different function each time) and the data is passed as a pointer
this will allow the following function signature:

func (b *Integer64ArrayBuilder) Append(val int64) error {
	r := C.array_builder_append_int(b.ptr, val.ptr)
	if r.err != nil {
		return errFromResult(r)
	}
	return nil
}

To be honest, now that I am writing this down I am not sure that the Go GC allows can promise that memory in the Go run time will be preserved during the C function run ( and C layer will need to copy that memory and not store it - a point of failure ) so maybe I'll need to think on a different technique .