[fpc-pascal] function returning a record vs paramaters
anton.tichawa at chello.at
Sat Jul 9 22:38:33 CEST 2005
>When a function requires that more than one value must be returned, what are the
>advantages of returning one of these values in a paramater versus using a record
>that contains all the data?
>A function needs to return an integer, string, and boolean. Why not just return
>a record containing an integer, string, and boolean?
When the integer, string, and boolean are logically related, and are
typically assigned, copied, allocated, stored or else processed as a
whole block, a record should be used anyway.
>Advantages of records:
> Surely records are much more legible code design than parameters.
Yes, especially in function calls, as in your example.
>Disadvantages of records:
> Are paramaters more portable than records, say if you were writing a library
>(.so or .dll, etc.)?
> Can a c++ or c program deal with a pascal record?
> How about speed and performance?
I think the best way is to pass the record as a var parameter, e. g.:
type t_my_record = record
procedure my_procedure(var a_record: t_my_record);
In this case, a simple pointer is passed to my_procedure. This is also
the way most C libraries work, passing a pointer to a structure.
When a function returns a record, an additional pointer parameter is
passed to it, invisibly to the pascal programmer, and the function fills
in the structure pointed to by that parameter.
For this reason, I personally tend to prefer a var-parameter: A function
returning a record looks like creating or allocating that record, which
is not true. A var-parameter shows, in pascal, a structure similar to
what happens on the machine code level. But it's a matter of taste, and,
of how the function result is used: When the result is often used as
part of expressions, or as a parameter to other procedures, the "result"
way is more legible than the "var-parameter" way.
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