C++ London Meetup: Tuppence more on Standard Algorithms

This evening of talks was split into a set of Lightning Talks in the first half followed by a discussion about the Standard Library in the second half.

Part 1 – Lightning Talks
Richard Chandler – ACCU 2018 Trip Report – much on C++14 and C++17 standards to catch up on as well as introduction to Kotlin and a number of talks on diversity and inclusivity.

Phil Nash – East End Story
Phil dived into the controversial East Const v West Const debate

    void f( T const& t ) // East const
    void f( const T& )   // West const

i.e. should you put the const before or after the type. This topic was introduced by Dan Saks in 2011 – Simplifying const Syntax, Dr Dobbs and revived by Jon Kalb in A Foolish Inconsistency.

“Const applies to what is on its left, unless there is nothing to the left, in which case it applies to what is on the right.” But using east const format, it always applies to the left! West const reads more naturally from left to right, e.g. “const integer” – the East const argument is that you would always read declarations inside out and right to left!

    char const * const pc = str // pc is a const pointer to a const char, reading right to left

Developers are already accustomed to using East const for const member functions (must put const on the ‘east’ side). And there are other examples of going East:

    // moving the return type further east as a result of c++11
    auto someFunc( int i ) -> std::string; 

    // you have to put the return type on the east side
    auto lambda = [] -> double { return 0; } 

Other considerations: Swift/Haskell have trailing return type; putting auto at the start of list of function definitions, the start of the names line up; C++ standard NL.26 says use conventional const notation, endorses West Const notation, but is itself inconsistent!

Phil is now using trailing return types everywhere in production code – see his blog, East End Functions (LevelOfIndirection.com)

Stewart Becker – A Fool’s Consistency, the rebuttal (Jonathan Muller’s talk)

East const gives more consistency? If 83% of people write const T (i.e. West const), you need to be consistent with everyone else in your codebase.
Const pointer to const fallacy – with modern c++, use const std::string_view instead. Can use std::as_const(x) to get the const cast.
Right-to-left fallacy – but we read loops etc from left to right, and ‘const’ is an adjective which goes before the noun in English.
Clockwise-Spiral rule for function pointers.

const east west const – you are allowed to write const in both the East and West positions!!

Part 2 – Tuppence More on Standard Algorithms – Iakov Sergeev
Iakov believes the standard algorithms should make code easier to implement and read, but are forgotten in practice. He raised issues with inconsistencies and the learning curve to use STL (output iterator, predicates, modifying input sequences, could take both begin/end iterators).

Historically, the predicates were hard to implement where you had to supply a functor to call algorithms. Now, with lambdas, it’s much easier and localised to call algorithms.

The audience felt that Eric Niebler’s work on the Ranges TS should help a lot with adoption of standard algorithms.

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