Some people do something like this:

--If object doesn't exist, create a dummy object

IF OBJECT_ID('dbo.InexistentFunction') IS NULL

EXEC('CREATE FUNCTION InexistentFunction()

RETURNS int

AS

BEGIN

RETURN 0

END')

GO

--Simply alter the object to get the correct definition.

ALTER FUNCTION dbo.InexistentFunction

(

@MyParam int

)

RETURNS date

AS

BEGIN

RETURN DATEADD( dd, @MyParam, GETDATE())

END

GO

--Test

SELECT dbo.InexistentFunction(10)

--Cleanup (just for this example)

DROP FUNCTION InexistentFunction