The CppCon 2015 conference program has been posted for the upcoming September conference. We’ve received requests that the program continue to be posted in “bite-sized” posts, a few sessions at a time, to make the 100+ sessions easier to absorb, so here is another set of talks. This series of posts will conclude once the entire conference program has been posted in this way.

The C++ possess another language inside it: the template language. It is useful for a lot of things, from writting less code to compile time computations or checks, but can lengthen compile time too. To master it is not easy.

The following interrelated CppCon 2015 talks tackle these issues and more (part 2).

In this post:

• Compile-time tools supporting generic programming in C++
• C++ metaprogramming: a paradigm shift
• Pruning Error Messages From Your C++ Template Code
• C++ Metaprogramming: Journey from simple to insanity and back
• boo{stache} exposed : the inner-workings of a generic template engine

Compile-time tools supporting generic programming in C++

Generic programming is a programming paradigm which makes it possible to build highly extensible and efficient libraries. In C++ it can be implemented using templates, therefore developers and users of generic libraries need to understand how the compiler works with templates. The details are important when the code using a library instantiates different templates (or specialisations), or the same templates but with different arguments as expected. Fixing such bugs can lead to difficult debugging sessions. These are not bugs in the program's runtime behaviour. These are bugs in the program's compile-time behaviour and therefore different tools are needed to find them. Tools providing insight into what happens during the compilation process are needed.

Template metaprogrammers have been pushing the limits of what is possible using templates. The way they use templates is usually more complex than what generic libraries need. Recently a number of advanced tools supporting template metaprogrammers have been built. REPL shells, debuggers, profilers are available to make it possible to see what happens during compilation.

This talk presents how these tools can be used and be useful for the developers and users of generic libraries. Insight into what happens inside the compiler can be extremely useful to understand why the code compiles slowly, behaves the way it does or to debug errors in code using generic libraries.

C++ metaprogramming: a paradigm shift

Most people think metaprogramming is hard. It isn't; we just didn't have the right tools for it. This talk will present a new way of metaprogramming using the same syntax as that of normal C++. It will show how the runtime and the compile-time boundaries can be crossed almost seamlessly. It will show how compilation times can be reduced without sacrificing expressiveness. It will introduce Hana [1], a newly accepted Boost library using cutting edge features of the language in a creative way to solve the problem of metaprogramming for good.

[1]: http://github.com/ldionne/hana

Pruning Error Messages From Your C++ Template Code

Many template libraries are regarded with ambivalent feelings by developers: On the one hand, such libraries can offer wonderful functionality. On the other hand, they are dreaded for the sheer amount of error messages spilled out by the compiler when there is even a small bug in the developer's code. This talk will demonstrate several techniques to drastically reduce the amount of compiler output in case of errors (with real-life examples, of course).

C++ Metaprogramming: Journey from simple to insanity and back

Part I: Introduction to template metaprogramming. Template metaprogramming is a variant of generic programming, a technique that uses C++ template mechanism to perform computations at compilation time, usually to generate, from a single description, executable code that depends on the properties of the data types. It can be viewed as “programming with types”. In this example-driven class we start with the overview of the metaprogramming tools (everything you wanted to know about template specializations but were afraid to ask). We will apply these tools to simple examples, such as: how to sort a sequence in order of increasing values, unless it’s a sequence of pointers, in which case we want the values of what they point to. Part II: Advanced techniques and practical applications. Simple examples of metaprogramming are fun and useful, but once you master them you start chafing at the limitations. This is C++, where we don’t suffer limitations gladly. We therefore move on to the more advanced techniques, including SFINAE, and the appropriately more advanced examples. The journey takes us back to the beginning: after all, when sorting a sequence of values vs a sequence of pointers, you don’t really care whether the pointer is smart or dumb. What you really want to know is whether “*p” compiles or not. What you really need is an “if_compiles” metaprogramming function.

boo{stache} exposed : the inner-workings of a generic template engine

Template engines are commonly found generating web pages, customer reports, or even source code. They take a source template and data model as input and generate some desired output.

Boostache was started as the Library in a Week challenge from CppNow'14 with initial support for Mustache.

Today Boostache supports multiple template formats and adapts automagically at compile time to user defined data models. Many of the techniques utilized in Boostache are the same that Ciere has employed in custom IDL compilers, Domain Specific Language systems, compilers, and runtimes.

This talk will briefly introduce Boostache and then delve into the internal architecture and design of the library. We will explore some implementation details of the parser, compiler, virtual machine, and generic data model infrastructure with the goal to expose useful techniques and patterns from this C++11 code base that can be used in your own libraries and applications.