Quick Q: How do I remove a unique_ptr from a queue? -- StackOverflow

By Blog Staff | Jul 8, 2013 11:39 AM | Tags: basics

Quick A: move(q.front()).

remove unique_ptr from queue

I'm trying to figure out how/if I can use unique_ptr in a queue.

// create queue
std::queue<std::unique_ptr<int>> q;

// add element
std::unique_ptr<int> p (new int{123});
q.push(std::move(p));

// try to grab the element
auto p2 = foo_queue.front();
q.pop();

I do understand why the code above doesn't work. Since the front & pop are 2 separate steps, the element cannot be moved. Is there a way to do this?

Living with Lambdas -- Alfons Haffmans

By Blog Staff | Jul 8, 2013 03:31 AM | Tags: advanced

We have such a powerful language, and what a powerful language it is.

Living with Lambdas

by Alfons Haffmans

From the article:

You can work in the functional programming paradigm in C++. And you may be surprised at how complete C++’s support for functional programming is.

... C++ has always been a multi-paradigm language. And while previous attempts to add practical functional programming features required significant effort, recent additions to the C++ standard, like lambdas, have improved the situation. This paper explores the out-of-box support for functional programming provided by the new standard. We’ll look at techniques typically found in introductory functional programming textbooks. This article assumes familiarity with C++, but not necessarily with basic functional programming.

The source code is available in github and is compiled using gcc 4.8 installed on Mac OSX using MacPorts.

Quick Q: What are move semantics? -- StackOverflow

By Blog Staff | Jul 6, 2013 05:22 AM | Tags: basics

One of the highest-ranked C++ questions (and answers) on StackOverflow is worth re-reading if you're new to the topic:

What are move semantics?

I just finished listening to the Software Engineering talk radio podcast interview with Scott Meyers regarding C++0x. Most of the new features made sense to me, and I am actually excited about C++0x now, with the exception of one. I still don't get move semantics... What are they exactly?

Moving an Object Does Not Destroy The Original -- Andrew Koenig

By Blog Staff | Jul 5, 2013 04:17 PM | Tags: basics

Andy's next on move semantics:

Moving an Object Does Not Destroy The Original

by Andrew Koenig

From the article:

Recall first that objects are generally moved instead of copied because the originals are about to go away. When I learned this fact, I thought at first that moving an object should destroy the original. ...

I was surprised to learn that that is not what happens. Instead, whenever a program moves an object, it must leave that object with a valid value so that it can be destroyed later. ...

Modern C++ Programming with Test-Driven Development -- Jeff Langr

By Tom Kirby-Green | Jul 3, 2013 04:16 AM | Tags: tdd intermediate

[Ed.: This upcoming book is currently in beta. Thanks Tom for pointing it out!]

I have nothing to do with this book other than I've bought the beta book and am enjoying it thus far. It fills a gap in the market very nicely.

Modern C++ Programming with Test-Driven Development: Code Better, Sleep Better

by Jeff Langr, edited by Michael Swaine

If you program in C++ you’ve been neglected. Test-driven development (TDD) is a modern software development practice that can dramatically reduce the number of defects in systems, produce more maintainable code, and give you the confidence to change your software to meet changing needs. But C++ programmers have been ignored by those promoting TDD -- until now. In this book, Jeff Langr gives you hands-on lessons in the challenges and rewards of doing TDD in C++.

Auto: A Necessary Evil? -- Roger Orr

By fbuontempo | Jul 2, 2013 02:05 PM | Tags: intermediate basics

Roger Orr has written about the history and use of auto in ACCU's Overload 115:

Auto -- A Necessary Evil?

by Roger Orr

From the article:

The keyword auto now lets you declare variables where the compiler provides the actual type and the programmer is either unwilling or unable to name the actual type. The keyword can also be used in function definitions to let you provide the return type after the rest of the function declaration, which is useful when the return type depends on the type of the arguments.

As with any new keyword there are questions about usage –- at two levels. First of all, where and how are programmers permitted to use the new feature. Secondly, what guidance is there to sensible adoption of the new feature. I intend to start with by answering the first question and then subsequently focus on the second.

Summer standards papers mailing available

By Blog Staff | Jul 2, 2013 10:10 AM | Tags: None

Note: Some of these papers explore potential future standardization directions and alternatives. They do not discuss or propose to amend the C++14 Committee Draft paper whose ballot is currently in progress.

The official mid-meeting standards papers mailing is now available. If you are not currently a committee member, please direct discussion about these papers to the public std-proposals forum.

Note: Most or all of these papers have also been posted already to this site’s Standardization RSS feed.

New paper: N3703, Extending std::search to use Additional Searching Algorithms (v3) -- Marshall Clow

By Blog Staff | Jul 2, 2013 10:05 AM | Tags: experimental

Note: This paper explores potential future standardization directions and alternatives. It does not discuss or propose to amend the C++14 Committee Draft paper whose ballot is currently in progress.

A new WG21 paper is available. A copy is linked below, and the paper will also appear in the next normal WG21 mailing. If you are not a committee member, please use the comments section below or the std-proposals forum for public discussion.

Document number: N3703

Date: 2013-06-28

Extending std::search to use Additional Searching Algorithms (Version 3)

by Marshall Clow

Excerpt:

Note:

• This is an update of n3606, presented in Portland. The major differences are support for comparison predicates in Boyer-Moore and Boyer-Moore-Horspool, and wording for the standard.
• n3606 was an update of n3411, presented in Portland. The major difference is a different interface for the search functions.

[...]

std::search is a powerful tool for searching sequences, but there are lots of other search algorithms in the literature. For specialized tasks, some of them perform significantly better than std::search. In general, they do this by precomputing statistics about the pattern to be searched for, betting that this time can be made up during the search.

The basic principle is to break the search operation into two parts; the first part creates a "search object", which is specific to the pattern being searched for, and then the search object is passed, along with the data being searched, to std::search.

This is done by adding an additional overload to std::search, and some additional functions to create the search objects. ...

New paper: N3702 Introducing an optional parameter for mem_fn -- Mikhail Semenov

By Blog Staff | Jul 2, 2013 10:02 AM | Tags: experimental

Note: This paper explores potential future standardization directions and alternatives. It does not discuss or propose to amend the C++14 Committee Draft paper whose ballot is currently in progress.

A new WG21 paper is available. A copy is linked below, and the paper will also appear in the next normal WG21 mailing. If you are not a committee member, please use the comments section below or the std-proposals forum for public discussion.

Document number: N3702

Date: 2013-06-28

Introducing an optional parameter for mem_fn, which allows to bind an object to its member function

by Mikhail Semenov

Excerpt:

When a member function is used as a parameter to another function (the latter is usually called a functional) it is often necessary to provide the corresponding class object as a parameter as well. But functionals, like for example an integral, are often written to accept one global function. In cases when a member function and an object are needed, it is necessary to bind them together,  so that the result can be supplied to the corresponding functional as one parameter. ...

... The proposal is to allow mem_fn to accept a second, optional parameter.

New paper: N3701, Concepts Lite (2nd revision) -- A. Sutton, B. Stroustrup, G. Dos Reis

By Blog Staff | Jul 2, 2013 09:56 AM | Tags: experimental

Note: This paper explores potential future standardization directions and alternatives. It does not discuss or propose to amend the C++14 Committee Draft paper whose ballot is currently in progress.

A new WG21 paper is available. A copy is linked below, and the paper will also appear in the next normal WG21 mailing. If you are not a committee member, please use the comments section below or the std-proposals forum for public discussion.

Document number: N3701

Date: 2013-06-28

Concepts Lite (2nd revision)

by A. Sutton, B. Stroustrup, G. Dos Reis

Excerpt:

This paper is in its 2nd revision. There have been a number of substantial
changes, which are summarize here.

• The syntax of constrained member functions has changed.
• The syntax of the requires expression has changed.
• We have introduced syntax for constraining generic lambdas, and using constraints wherever auto is used.
• We allow the use of overload sets as arguments to constrained functions.
• The standard wording has been more extensively developed, but does not yet include language for constrained generic lambdas.

This paper is organized like this:

• Tutorial: introduces the new features specified by Concepts Lite, their core concepts and examples.
• User’s guide: provides a more extensive discussion of the proposed features and demonstrates the completeness of the constraints mechanism. We also include some high-level discussion of the language mechanics.
• Discussion: explains what constrains are not. In particular, we try to outline constraint’s relation to concepts and to dispel some common misconceptions about concepts.
• Design Notes: Notes on the design of terse notation for templates and generic lambdas.
• Language definition: presents a semi-formal definition of constraints