try catch in swift and variable visibility

fileio.swift

func mySimpleFileRead(path: String) throws -> UnitsData {
        
    let fileName = (path as NSString).expandingTildeInPath
    let url = URL(fileURLWithPath: fileName)
   
    let data = try Data(contentsOf: url)
    return try JSONDecoder().decode(UnitsData.self, from: data)
}

main.swift

var unitsData2: UnitsData
do {
        unitsData2 = try mySimpleFileRead(path: "~/progs/myxcode/ogrev1/ogrev1/ogrev1/units.json")
} catch {
        throws JFDFileError.JSONDecodeFailed

}
    
    print("=-+-+==.name is \(unitsData2.units[1].name)")