For convenience I'm trying to add an extra property to CountryData
Unprotect[CountryData];
CountryData[c_String, "MyProperty"] := 0; (* actually call to another function *)
Protect[CountryData];
But when using it I get:
CountryData["Greenland", "MyProperty"]
CountryData::notprop: "!(\"\\"MyProperty\\"\") is not a known property for CountryData. Use CountryData[\"Properties\"] for a list of properties."
What's the right way to do this?
There is high probability this is a duplicate, but I wasn't able to find how to do this, sorry in advance