Tuples -- who needs 'em

[Gordon McMillan]

Martijn Faassen wrote:

[discussing the need for tuples with Bob Alexander]

> Okay, but it's generally practiced in idiom. 
[snip]
> ... I think it's more
> than just the dictionary key argument.

Very true. There are 2 technical arguments for tuples 
(dictionary keys and efficiency); both are weak. The main 
difference is idiomatic.

[Bob]
> > There have been cases where I used tuples, to find out
> > later that I wanted mutability, so went back and changed.
> 
> Hm, I rarely if ever seem to run into this. If I need mutability of
> a set of heterogenous objects I tend to use a class. There may be a 
> switch from tuples to classes, but not often from tuples to lists, I 
> think.

That's because you understand the idiom, Martijn. Lists are 
collections. The competing choice to a list is a dictionary. 
Tuples are toy structs; the competing choice is a class.

Experience tells me that trying to use a list where a tuple is 
needed will yield either unsafe or safe but bloated code. No 
technical reason; it's just that lists (as collections) will 
eventually be mutated in a way that's natural for collections, 
but disastrous where the purpose is struct-like.
 
> > This sort of thing
> > happens in exploratory programming, so when in that mode one might want to
> > use lists unless one is really sure in advance that tuples are the right
> > thing.

By all means, use lists whenever you're unsure. You'll soon 
come to recognize when a tuple is more appropriate. It won't 
take long (it couldn't, Martijn's too young to have taken long to 
learn anything <wink>).
 


- Gordon