You work in a bar, pouring pints for the locals. One of your regulars comes in; he’s looking pretty grumpy today. “Whiskey” he snaps. You put down a glass and pour. You finish pouring and he necks back the drink. “Again”, he snaps. Again, you pour and as soon as you finish he necks it. This repeats two or three more times before the grumpy man slams down the money for his tab and leaves. Congratulations, you have just taken part in a “Producer/Consumer” exchange.
The C++11 standard introduced so called Variadic Templates. These have many uses, one of which is the ability to write functions that take any number of arguments without having to mess around with C-style non-type safe “var-args” and printf like format specifiers.
In my previous article I discussed the difference between up-cast and down-cast and explained why down-casting is rarely a good idea (or even necessary). That said, there are a few times when down-casting is valid and so this article shows how to do so, safely, in C++.
When working with objects that have an inheritance model you basically have an inverted tree that represents your object hierarchy. Contrary to a normal everyday trees, an inheritance tree has its root at the top. In other words, the root of the tree represents the base class and anything below it represents a more derived class. Continue reading “Bloodlines and casting”
One of the problems any developer will eventually have to resolve is one of latency; specifically, being able to retrieve and process data in a timely fashion. This issue can come in many guises but they generally manifest as needing to read data from a backing store that cannot deliver the high performance needed by the application. This can be a tricky problem to solve but the general method is to implement some form of caching. The remainder of this article will discuss one caching mechanism, called the LRU Cache.
Imaging you have a map and on that map you define a bunch of geo-locations; polygons, which are defined by their vertices as latitude and longitude co-ordinates. These geo-locations may overlap and may either be very big or very small (or in-between). The problem is to figure out, for any point on the map, which of these geo-locations bound it.
The C and C++ standards documents can be a bit of a beast to trawl through and quite often you’ll find yourself reading the same sentence a number of times trying to fathom out what it is actually saying. It’s just like when you read the EULA for a software product; lots of big words and long sentences that don’t actually seem to make a lot of sense.
The C++03 standard treats temporary types as r-values (types only meant to go on the right hand side of an assignment expression). As such, it is only possible to bind a temporary to a const reference type. This is a somewhat arbitrary and, often, frustrating rule. The original idea was that there would be no good reason to modify a temporary; however, it turns out that there are plenty of good reasons for doing so and this arbitrary restriction was just a nuisance that served no good cause.
In case you’ve never heard of it before, Boost is a set of peer reviewed libraries for C++. They provide a lot of features that are sorely missing from the standard C++ libraries and are probably the closest C++ developers have to a standard development toolkit. In fact, Boost is so useful that a number of the projects were included in the C++11 standard.
A good friend of my asked me how to get started in meta-template programming. Of course, the first thing is to know C++ and know it well. Other than that, I think my best advise is to ensure you completely understand how the C++ template generation process works. For example, if you don’t know what SFINAE stands for you’re probably not really to start writing meta-templates (of course, that doesn’t mean you are not ready to start learning).