lubkoll / type_erasure

type_erasure

This repo serves multiple purposes.

• First, it contains several "hand-rolled" implementations of the same erased type, for reference.

• Second, it includes the "Type Erasure" presentation given at CppCon 2014.

• Third, it contains the emtypen tool, which generates type erasure code based on a user-supplied implementation form.

Skip to the relevant section below, depending on what you came here for. Build instructions can be found at the end.

Reference Implmentations

Check out the hand_rolled and boost_type_erasure directories for examples of various approaches to type erasure. Note that there are emtypen form and header files for most of the approaches -- everything but the manual v-table and Boost.TypeErasure approaches. All examples were written against the C++11 standard.

Presentation

If you want to look at the presentation slides live in the tubes, go to:

http://tzlaine.github.io/type_erasure

Otherwise, the CppCon 2014 presentation can be found in index.html, with the supporting files found in the presentation directory. Point your browser at index.html and get ready to rumble. I don't know why I said that last part.

emtypen

emtypen generates C++ code for one or more "erased types" (types that can hold anything that fits a given interface) from a C++ header that defines the required interface(s). It performs this magic by asking the libclang library (a wrapper around the Clang front end) what is in the given C++ header. Detailed usage instructions can be found by passing --help or --manual to emtypen.

A pre-built Windows installer is available here.

A pre-built Mac OS (Mavericks only) installer is available here.

Build Instructions

First, note that the code in this repo is written against the C++11 standard. It is known to work with Clang 3.4, GCC 4.9, and Visual Studio 2013. It may work with earier versions of Clang or GCC, but will not work with any earlier version of Visual Studio.

To build the entire project, simply install CMake 3.0 and use it to build this repo. Specific steps are given at the end.

Many of the examples have coverage tests that require headers from Boost.Test. The Boost.TypeErasure example also obviously requires Boost. Neither requires a compiled Boost library; the headers will suffice. If you want to build these items, define the CMake variable BOOST_ROOT (see below). If you do not want to build these items, it won't break anything not to define BOOST_ROOT.

emtypen requires libclang headers and libs. If you want to build emtypen, define the CMake variable CLANG_ROOT (see below). If you do not want to build emtypen, it won't break anything not to define CLANG_ROOT. At the time of this writing, there are no pre-built Clang binaries built with Visual Studio 2013, but it's now very easy to build Clang from source with Visual Studio. There's a small wrinkle, however. CMake doesn't like import libs with extensions other than .lib, and libclang's is built as libclang.imp. There's probably some obscure CMake incantation that fixes this, but it's easier just to rename libclang.imp to libclang.lib.

If you build Clang from sources, it will make your life much easier to install it somewhere, and then set CLANG_ROOT to the installed location. This will set up the directory structure expected by the emtypen build; the structure of the build products for the built-in-place Clang is different.

Here are the specific steps to build this repo with CMake. It is assumed that this repo has been cloned into a directory caled "type_erasure":

• From a command shell, create a directory into which the build products will be generated, e.g. type_erasure/build.

• Move into the build directory.

• Execute cmake <path> [-DBOOST_ROOT=<path_to_boost>] [-DCLANG_ROOT=<path_to_clang>, where <path> is the relative path from your build directory to "type_erasure", e.g. ...

This will generate your build files. On UNIX-like systems this will default to generating makefiles, and on Windows this will default to generating Visual Studio solution files. You know what to do from here.