[Development] RFC: Containers member functions for algorithm

Milian Wolff milian.wolff at kdab.com
Thu Mar 23 15:10:56 CET 2017

On Thursday, March 23, 2017 11:12:31 AM CET Giuseppe D'Angelo wrote:
> Il 23/03/2017 10:50, Philippe ha scritto:
> > I hardly imagine a "container" api without a "contains()" member. What I
> > would call good sense. Qt already has this, std not.
> > 
> > The other member that makes sense, if "indexOf()"... Qt already has this.
> Bikeshedding: this implies that your container contains a type
> comparable for equality, but no sequential container enforces that (nor
> it should), so this is effectively API pollution.
> Bikeshedding²: this also means more symbols exported (if you end up
> exporting an instantiation of the container), or similarly more totally
> unnecessary requirements on the type (cf. the QItemSelection example)
> Bikeshedding³: contains()/indexOf() use a linear scan, where's my member
> function for binary search, if I know the container is sorted? How can I
> decide the direction of the linear scan?
> Bikeshedding⁴: what are the parameters of contains()/indexOf() for a
> Container<T>? T / const T &? But why not any K that you can compare
> against a T?
> Bikeshedding⁵: if there's indexOf() (returning an index), should there
> it be also a find() (returning an iterator)? If there's find(), should
> it there also be an indexOf()? Is it OK to have fundamentally duplicated
> APIs, and not strive for a good degree of minimality and simplicity?
> [we can go forward]

I'm very much with Peppe here. Olivier, please take these points into 
consideration. Bloating the API of a generic container with methods that are 
only usable for special circumstances is imo not a good idea.

I am not opposed to having free functions which are giving you convenience. 
That's also what many of the existing convenience functions should have been 
in the first place, btw. Like QStringList::join etc.

Milian Wolff | milian.wolff at kdab.com | Software Engineer
KDAB (Deutschland) GmbH&Co KG, a KDAB Group company
Tel: +49-30-521325470
KDAB - The Qt Experts

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