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Subject: Re: [boost] [range] [general] making member functionsSFINAE-friendly
From: Vadim Stadnik (vadimstdk_at_[hidden])
Date: 2013-02-19 05:04:53

On Tue, Feb 19, 2013 at 4:17 PM, Nathan Ridge <zeratul976_at_[hidden]>wrote:

> This was discussed upthread. To summarize, the standard library
> makes the design choice of not providing certain operations
> if they cannot be implemented with a certain asymptotic
> complexity (for example, subtraction of two iterators if it
> cannot be implemented in constant time), and Boost is trying
> to be consistent with this design choice.
I agree that consistency of the library design is important, but the case
is not completely trivial. IMO, this design principle is only a theoretical
one. In practice, it is often unhelpful and counterproductive. Because of
this principle, STL and C++ miss the big selling point.

An end user (who pays for and uses a software product) is interested in the
best running time of an algorithm which is determined not only by costs of
specific operations, but also by their frequencies. Relatively small number
of inefficient operations does not affect the total computational cost of
an algorithm.

Also, this design principle makes illegal advanced and/or augmented data
structures which are beneficial for many complex algorithms. For example,
insert() and erase() functions for a single element with O(log N) cost are
not allowed by the C++ standard, however, significantly less efficient O(N)
operations are allowed for std::vector.

I think that the current standard specifications for computational
complexities of operations are to some degree obsolete. They create
unnecessary restrictions that will be either amended or removed completely
in future versions of STL.

Vadim Stadnik

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