Category: C++

(Start at the beginning of the series if you want more context.) Generalising iota To pretty-print a reversible polynomial, we need to provide for reversibility of iota. So what is iota? It makes a range by repeatedly incrementing a value. What if instead of increment, we use an arbitrary function?…

(Start at the beginning of the series if you want more context.) On reversibility It occurs to me that I’ve been touting reversibility as a good thing, both implicitly and explicitly (for polynomials), and the reason for that is not just that I might want to print polynomials in natural…

(Start at the beginning of the series if you want more context.) So, I was going to implement monoidal_zip, and to do that, I would clone zip_with.hpp. So I did that. Eric’s a great library author, and the ranges code is pretty easy to read. For the most part I…

(Start at the beginning of the series if you want more context.) First steps with power series A power series (or polynomial, to give it a more familiar term in the case where it’s finite) is represented simply as a sequence of coefficients of increasing powers of x. This is…

The idea For some time since attending C++Now, I have been meaning to get around to playing with Eric Niebler’s range library. Eric presented ranges in a worked example as one of the keynotes at C++Now – a prior version of the talk that he gave at the Northwest C++…

I just got back from C++Now, an excellent conference where C++ template metaprogramming experts abound. A phrase I overheard often was “the lambda trick”. It’s a trick for speeding up compiles when templates get deep. Every C++ programmer knows that deep templates can slow down compilation. Most assume that this…

One can assign a lambda to auto or to std::function. Normally one would assign a lambda to auto to avoid possible unwanted allocation from std::function. But if you want recursion, you need to be able to refer to the lambda variable inside the lambda, and you can’t do that if…

These days, it’s easy to do the right thing. Don’t do this: Don’t use std::rand(). Ever. Don’t use std::random_shuffle() to permute containers. (Too easy to misuse; can use std::rand() under the hood.) Don’t use any kind of clock for a seed. Don’t use mod (%) to get a random value…

C++ provides a strange mix of compile-time and runtime functionality for dealing with tuples. There are some interesting parts, like std::tie to destructure a tuple, and std::tuple_cat to join together several tuples into one. So there is evidence that the standard has been influenced by some functional programming ideas, but…

Myth: Lambda expressions can cause heap allocations. I see this myth coming up a lot. People think that lambdas can cause a heap allocation – on Reddit, on StackOverflow, on Channel9 comments, in personal conversations. I don’t blame people for thinking this – C++ is complex. But it always seems…