Обсуждение: Creating operators
Since no one replied in pg-general, I am reposting to hackers. Q1: Let's say I want to create a '+' operator for <my own type> + int4. Do I really have to define two '+' operators, one <my own type> + int and the other int + <my own type> Q2: Can I create an operator '::', such as <my own type>::double ? Gene Sokolov.
"Gene Sokolov" <hook@aktrad.ru> writes: > Q1: > Let's say I want to create a '+' operator for <my own type> + int4. Do I > really have to > define two '+' operators, one > <my own type> + int > and the other > int + <my own type> Yes. There's nothing compelling them to behave the same, after all (consider '-' instead of '+'). If they do behave the same you should indicate this with "commutator" links --- see the discussion in the manual. > Can I create an operator '::', such as <my own type>::double ? You can't redefine the meaning of the typecast construct '::', if that's what you meant. But perhaps what you really meant was that you want to provide a conversion from your type to double. For that you just make a function named 'double', yielding double, and taking your type as input. The typecast code will use it automatically. (Of course "double" is spelled "float8" in Postgres-land, but you knew that...) regards, tom lane
> > Can I create an operator '::', such as <my own type>::double ? This brings up something: I see mention in Date and Darwen of an SQL3 enumerated type. Nice feature, but they show the syntax being: <type>::<value> which reuses the "::" operator in a way which may be incompatible with Postgres' usage (seems to me to have the fields reversed). btw, I could imagine implementing enumerated types as Postgres arrays or as a separate table per type. Has anyone come across this SQL3 feature yet? Any opinions?? - Thomas -- Thomas Lockhart lockhart@alumni.caltech.edu South Pasadena, California