## Reporting Coordinate Transformations

We have already seen (§4.8) how the boolean (integer) ReportReport attribute of a MappingMapping works. If it is non-zero, the operation of transforming a set of coordinates will result in a report being written to standard output. This will display the coordinate values before and after transformation. It can save considerable time during program development by eliminating the need to add loops and output statements to your program.

In a finished program, however, you should be careful that the Report attribute is not set to a non-zero value unless you want to see the output (there may often be rather a lot of this!). To help prevent unwanted output being produced by accident, the Report attribute is unusual in that its value is not preserved when a Mapping is copied using astCopyastCopy (§4.13). Instead, it reverts to its default of zero (i.e. un-set) in the copy. It also reverts to zero when a Mapping is written out, e.g. to a file using a ChannelChannel (§15).