pub fn returns(mut self, type_: DataType, as_ref: bool, allow_null: bool) -> Self {
        self.retval = Some(type_);
        self.ret_as_ref = as_ref;
        self.ret_as_null = allow_null;
        self
    }
Sets the return value of the function.

# Parameters

* `type_` - The return type of the function.
* `as_ref` - Whether the function returns a reference.
* `allow_null` - Whether the function return value is nullable.
src/builders/function.rs