examples/date_arithmetic: Add an example that shows of date arithmetic

diff --git a/examples/date_arithmetic.lua b/examples/date_arithmetic.lua
new file mode 100644 (file)
index 0000000..3b1126d
--- /dev/null
+++ b/examples/date_arithmetic.lua
@@ -0,0 +1,33 @@
+local luatz = require "luatz"
+
+-- We do this a few times ==> Convert a timestamp to timetable and normalise
+local function ts2tt ( ts )
+       return luatz.timetable.new_from_timestamp ( ts ):normalise ( )
+end
+
+-- Get the current time in UTC
+local utcnow = luatz.time ( )
+local now = ts2tt ( utcnow )
+print ( now , "now (UTC)" )
+
+-- Get a new time object 6 months from now
+local x = now:clone ( )
+x.month = x.month + 6
+x:normalise ( )
+print ( x , "6 months from now" )
+
+-- Find out what time it is in Melbourne at the moment
+local melbourne = luatz.get_tz ( "Australia/Melbourne" )
+local now_in_melbourne = ts2tt ( melbourne:localise ( utcnow ) )
+print ( now_in_melbourne , "Melbourne" )
+
+-- Six months from now in melbourne (so month is incremented; but still the same time)
+local m = now_in_melbourne:clone ( )
+m.month = m.month + 6
+m:normalise ( )
+print ( m , "6 months from now in melbourne" )
+
+-- Convert time back to utc; a daylight savings transition may have taken place!
+-- There may be 2 results, but for we'll ignore the second possibility
+local c1 , c2 = melbourne:utctime ( m:timestamp( ) )
+print ( ts2tt ( c1 ) , "6 months from now in melbourne converted to utc" )