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Cello High Level C

Best Improvements of Cello 2.0

Fat Pointers

The complete internal workings of Cello have been rewritten and now it uses the concept of fat pointers to ensure Cello Pointers are fully compatible with standard C pointers. This is a massive win for interoperation with standard C because it means you can use Cello objects with standard C functions and types. No longer are you forced to use typeless pointers when you don't want to and Cello really does work on top of normal C, not orthogonal to it.

Type Definitions

The overhead of declaring a structure Cello compatible has been reduced from 20 or 30 lines of code to just one. Not only this but there are a huge number of operations Cello has defaults for now. In one line of code you can suddenly make it so that an object is usable across the whole Cello infrastructure including garbage collection, data structures, IO, and much more. Combined with C compatibility now you there is really nothing to lose by making your C structures Cello compatible. One line and you're ready to go.


It is fair to say that Cello 1.0 was insanely slow. It had some pretty terrible data structures and the overhead of calling Cello functions inside a tight loop was massive.

In Cello 2.0 all the data structures have been updated to be modern, fast, and efficient. Cello has also been heavily optimised and benchmarked to ensure it doesn't have too much of a performance penalty. Currently it sits between C and Java on most operations. The better interop with C has also helped in this regard, making it easy to drop down to C for numerical calculations and other performance intensive areas. And if you still need that extra performance remember that all C programs are also valid Cello programs!


Cello 2.0 only relies on a couple of fairly standard C language extensions. Namely the dollars in identifiers extension and the gnu variadic macros extension.

Unfortunately this does mean that closures were been dropped from the features list since 1.0, but it seems like a sensible omission as now Cello can be compiled easily with all of the major compilers including gcc, clang, cl.exe, and tcc (on the development branch).

Several of the defines Cello 1.0 made such as local and global have also been dropped. While these are certainly more readable than static and extern the potential for shadowing issues, and the fact that I wanted Cello to play nicely with C in this release, outweighed the benefits.

In general programming in Cello feels a lot less like a different language and more like an augmented C.


Having a runtime layer isn't just good for high level programming - it also provides an easy way to insert all of the runtime checks that are missing from standard C programming. These are everywhere in Cello. It performs out of bounds checks, out of memory checks, IO checks, and much more. If there is a runtime error an exception will be thrown with a nice error message and a stack trace.

Of course once you're program is running correctly all of these checks can be disabled using -DCELLO_NDEBUG to get C style performance.

All of the documentation is now built into Cello and can be accessed via the help function. Even the website documentation is generated using a simple C script.


Cello Documentation is now built into the language. In fact - the website documentation is just generated using a simple Cello script. Having the documentation available from the library is nice (you can just call help on some type), but more importantly because the code and documentation is in the same place there is less chance of it getting out of sync - all pull requests go to the main repo.


The new version of Cello has python3 style iterables. Although the syntax isn't as nice as python this does mean you can do neat things like use slices, filters, and maps on any iterable type. Special care has also been taken to ensure these types can be constructed on the stack so the overhead should be as small as possible.

Garbage Collection

One of the things I really wanted to try to add to Cello was optional Garbage Collection. Previously I had sworn that it would be impossible, but I started to get a few inklings about how it might be done (in some form or other) and after following on from those I managed to find a compromise that adds a kind of Garbage Collection for Cello objects and is both simple, and portable. Having Garbage Collection is a big win for usability. And the fact that the Garbage Collection is optional means it can be turned off for performance critical sections or ignored where it isn't useful.

More generally it means you can choose to program more like you are using a scripting language than a systems language with the worry of memory leaks.