Append shapefiles without creating a copy in memory

[gertcuykens]

Hi Jonas, as far as I understand, we can open a shapefile or create one but not append to one

shape, err := shp.Open("static-segments/segments.shp")
shape, err := shp.Create("new-static-segments/segments.shp", shp.MULTIPOINT)

Can we have a shape, err := shp.Append("static-segments/segments.shp", shp.MULTIPOINT) ?

Thanks

[fawick]

Good idea IMHO.

But why the shape type parameter for shp.Append()? Wouldn't the shape type be given by the existing file already? Or is your idea to have Append check and return an error if the type in the call to Append and the one in segments.shp do not match?

[gertcuykens]

yep you are 100% correct, sorry forgot about that :D

So it would be

shape, err := shp.Append("static-segments/segments.shp")

No type checking just the same Error handling as shp.Open does

[fawick]

@gertcuykens, @tdilo I invite you to test and review https://github.com/fawick/go-shp/tree/addAppend

[gertcuykens]

Any specific reason not to recycle err instead of er?

    er := &errReader{Reader: shp}
    w.bbox.MinX = readFloat64(er)
    w.bbox.MinY = readFloat64(er)
    w.bbox.MaxX = readFloat64(er)
    w.bbox.MaxY = readFloat64(er)
    if er.e != nil {
        return nil, fmt.Errorf("cannot read bounding box: %v", err)
    }

[fawick]

The reason is that readFloat64 does not return an error by itself. The errReader allow to check whether should could actually be read from in these four calls.to readFloat64.

On November 17, 2017 9:41:27 PM GMT+01:00, Gert Cuykens notifications@github.com wrote:

Any specific reason not to recycle err instead of er?

  er := &errReader{Reader: shp}
  w.bbox.MinX = readFloat64(er)
  w.bbox.MinY = readFloat64(er)
  w.bbox.MaxX = readFloat64(er)
  w.bbox.MaxY = readFloat64(er)
  if er.e != nil {
      return nil, fmt.Errorf("cannot read bounding box: %v", err)
  }

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[gertcuykens]

Ok i see maybe the last line should be

return nil, fmt.Errorf("cannot read bounding box: %v", er.e)

then ?

[fawick]

Yes, you're absolutely right, thank you, good catch! Fixed.