C3 0.8.4 The last renaming

C3 0.8.4 is now available. This release expands parameter reflection and contracts, adds configurable stack probing and stack protection, introduces iOS support, and brings a new collection type and stream utilities to the standard library.

This release is titled “The Last Renaming” because it very likely contains the final adjustments to C3’s keyword set – and I think we’ve finally got them right.

Changing keywords is hardly the best way to convey stability, but sometimes it is necessary. In C3's case 0.9.0 means syntactic freeze of the language, so getting the choice right in the 0.8.x cycle is vital.

Of course, as usual the old keywords will still work as part of the backwards compatibility with 0.8.3 and earlier, but moving to the new ones are recommended.

Language changes & improvements¶

Renaming preview for 0.9 – changing the -def family¶

faultdef and attrdef were introduced in 0.7.0 and constdef in 0.7.10. The idea was to unify them under an easy-to-remember "def" suffix. Unfortunately a downside is that this pushes them to retain a similar syntactic shape. After much discussion, we're experimentally introducing new names:

• faultdef -> excuse
• attrdef -> attrmacro
• constdef -> constset

excuse comes from the general terminology, where the fault returned for an empty optional is called the "excuse" in the documentation. That this becomes a keyword further cements that term. In addition, excuse gains a shape with {}, not supported by faultdef:

excuse
{
    MY_FAULT,
    SOME_ONE_ELSES_FAULT,
}

attrmacro was chosen because attrdef takes parameters and in general acts closer to a macro than an alias.

Both cenum and constset were considered. Eventually the latter won out because it establishes a stronger independent feature, whereas the cenum hints at it just being an "enum that works like in C", which isn't correct.

Note that attrdef, constdef and faultdef will work throughout the entire 0.8.x cycle. The new keywords are considered an experimental change, and will be evaluated until 0.9.0. It will become the standard in 0.9.0 only if it's decided that the names are an improvement.

Pinpointing @require failures¶

It is now possible to associate a requirement with a particular parameter by placing it in brackets after @require:

<*
 @require [a] a > 0 : "a must be greater than zero"
*>     
fn void example(int a)
{
    // ...
}

This lets diagnostics point directly to the argument responsible for a failed precondition, making contract failures easier to understand at the call site.

Parameter reflection¶

Parameter reflection is more capable in 0.8.4. $reflect(foo).param_struct and Foo::param_struct provide access to a function's parameters as a struct. This allows macros to build up calls by populating each field, and then use struct splat to make the call:

fn void foo(int a, double b) { }

fn void test()
{
    // The parameter struct has fields `a` and `b`
    var $ParamStruct = $reflect(foo).param_struct;
    // Create a struct 
    $ParamStruct s;
    // Populate them.
    s.a = 10;
    s.b = 2.3;
    // Use struct splatting to make the call
    foo(...s);
}

Parameters can now also carry @tag attributes, and reflected parameters support get_tag, tags, and has_tag.

It is also possible to inspect a parameter's default value through .default_value.

As part of this work, FooFn::params now returns reflected references rather than ReflectedParam values. Code using this reflection API may need to be updated.

Conditional aliases¶

Alias definitions now accept ternary expressions. This makes it possible to select an implementation using a feature flag without wrapping the alias in a separate conditional declaration:

alias foo = $feat(ABC) ? foo_1 : foo_2;

Compiler and toolchain¶

Stack hardening and the x86 red zone¶

C3 0.8.4 adds several controls for stack hardening. The new --stack-probe, --stack-probe-size, and --stack-protector options configure stack probing and stack-canary generation from the command line.

Individual functions and lambdas can override these settings with @stackprobe(level), @nostackprobe, @stackprotector(level), and @nostackprotector. Naked functions no longer receive stack protectors by default.

The new @noredzone attribute disables use of the x86-64 red zone for a function. As a temporary safety measure, functions on ELF x86-64 are emitted without red-zone use. ELF and COFF output also gained support for the dso_local attribute.

The --implicit-float setting provides control over the emission of floating-point operations. This is useful for low-level targets where implicitly generated floating-point instructions are undesirable.

Platform and build improvements¶

This release adds support for targeting iOS. LLVM compilation scheduling has also been adjusted so the largest modules are built first, helping make better use of parallel compilation.

Project target types benchmark and test now work correctly with c3c benchmark and c3c test, including targeted benchmark functions. Project names passed to c3c init may now contain -, and the new --keep-obj option preserves object files after building and linking.

The compiler can now warn about unused locals and parameters with --warn-unusedlocal and --warn-unusedparam. Diagnostics have been improved for incorrect panic-function names, excessively long source lines or underlines, and build options incorrectly written with =.

Faster slice equality¶

Equality comparisons between slices of flat types are now lowered to memcmp instead of scalar loops, reducing the cost of comparing suitable slices.

Standard Library Updates¶

Streams and collections¶

The standard library now includes CachedInStream and CachedOutStream, as well as the new std::collections::Tree collection.

InStream.read has been made consistent: it returns 0 at end of file instead of throwing io::EOF, and it now requires a non-empty destination buffer. Code which catches io::EOF from InStream.read should be updated to check the returned byte count instead.

Ranges gained a range::slice macro, and Path.is_link can be used to determine whether a path is a symbolic link.

Networking, logging and memory¶

Sockets can now report both ends of a connection through Socket.peer_address, Socket.peer_port, Socket.local_address, and Socket.local_port. Logging gained log::get_logger.

RefCounted has been reworked slightly to differentiate between finalization and freeing.

Thread pool changes¶

The old deprecated pool::ThreadPool is now disabled by default, and the new thread::ThreadPool is enabled by default. The old implementation is exposed as ThreadPoolOld, with -D OLD_THREADPOOL available for restoring the old name, for projects that do not want to change the name to ThreadPoolOld.

Fixes¶

This release fixes a broad set of compiler crashes and miscompilations, particularly around generics, vectors, bitstruct operations, default arguments, and deferred control flow.

Notable compiler fixes include:

• Generic declarations disabled with @feat are no longer instantiated.
• Generic aliases inside functions no longer cause the compiler to hang.
• Generic function pointers are resolved before use regardless of generic resolution order.
• Dead-code detection is preserved correctly when leaving a scope.
• A switch inside defer is no longer copied incorrectly during compilation.
• Debug information for default-initialized arguments and code generation for decrementing bitstruct fields no longer crash with LLVM 23.
• Struct initializers containing arrays of vectors are aligned correctly.
• Reversing vectors larger than 128 elements no longer corrupts the heap.
• $$mod on unsigned integers now emits an unsigned remainder operation.
• Optional-vector-to-array casts now generate correct code.
• Overloading from-end subscripts such as foo[^1] = 2 now works correctly.
• The configured C compiler is now used consistently.

The standard library also received several correctness fixes. Large left shifts now work for BigInt, copying a DString no longer overwrites its allocator, and FixedBlockPool handles changes to grow_capacity correctly. Fixes also landed for mem::equals, UTF-16 surrogate pairs in String.escape, virtual-memory reserve page sizes, and stale thread IDs returned by thread::current on POSIX.

String case-conversion attributes such as @str_pascalcase and @str_camelcase now retain digits instead of treating them as discarded word separators.

Thank yous¶

Again, this release wouldn't have been possible without the C3 community. I'd like to extend a deep thank you to everyone who contributed through code, issue reports, testing, and discussions.

PR contributors for this release¶

Stdlib: Archishman Nag, m0tholith, Manu Linares, Ricardo Tomasi, Senthilnathan, Velikiy Kirill.

Compiler & toolchain: Alexandru Paniș, Darvisim, Manu Linares, neerajnangireddy, rickyadastra, ssimb, Vyacheslav Denisov.

CI/Infrastructure: Darvisim, Fernando López Guevara, Manu Linares.

Change Log¶

Want To Dive Into C3?¶

Check out the documentation or download it and try it out.

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