I've run into this many times, and I think I've used all the
techniques you mention and some others less hygienic. I've been most
satisfied with your 2) and 3) solutions. There's not really that much
overhead in making a struct or Obj-C class for two specific kinds of
values, and once you've got it you know exactly what you're doing at
all times. I like structs becaus they're so lightweight, and I like
Obj-C classes (with properties, yay!) because structs are so ugly to
declare.
I note that Cocoa itself uses all these techniques, but maybe they
lean toward structs with a few specialized functions for working with
them, for constructs that will be used often like NSRange. On the
other hand there's NSIndexPath; since it's a class, UITableView can
create a category on it that provides properties. Very nice.
On Jul 2, 2008, at 11:48 AM, James Montgomerie wrote:
Say I have a method that needs to return two equally important
values (in my case, a string and an offset into it). I am
overthinking how to do it, and I though it would be interesting to
see what others have done.
I see these opportunities (my use of 'object' and 'value' is blurred
below, since I'm thinking of the abstract case - assume that both
values could be objects):
1) Just return the first value, and have the caller supply an
argument that the second value gets written into (akin to how
NSError is customarily used). This seems a bit unclean, since one
value is not more important than the other, and both are necessarily
returned.
2) Define a custom C struct (like NSRect, but with e.g. 'string' and
'offset' members) and return objects in it. Just like any other
returned objects, the caller would be expected to retain them
individually if it needed to keep them around.
3) Define a custom Obj-C class with two properties [e.g. 'string'
and 'offset'] and return an object of that class (with properties
appropriately set).
4) Create a 'Pair' C struct with two ids in it. Use it like the
custom struct in (2). This struct is more reusable than the one in
(2), so this solution seems less 'heavyweight', but it is less
descriptive.
5) Define a 'Pair' Obj-C class with 'first' and 'second' properties,
use as (3). Again, more reusable, less 'heavy' seeming than (3),
but less descriptive.
6) Return an NSArray with two items in it (this seems the least
descriptive option, from the point of view of someone reading the
header).
7) Return an NSDictionary with two items in it, keyed by their
property names. This seems a bit wasteful, since the dynamicisim of
a dictionary is not required, and is also not so descriptive from a
header-reading perspective.
Oh, and there's also 8) Rename the file .mm, and use a C++
std::pair<id, id> class. (Only joking :-)
How would you do this? Are there other, better options?
Jamie.
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