Can the new Clang Objective-C literals be redirected to custom classes?

Question

Although the overloading of @ begins to tread on dangerous territory, I love the addition of the new Objective-C literals in Clang 3.1. Unfortunately the new li

Answer 1

The comments have it all correct, but just to summarize:

• No.

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The meanings of Apple's @{}, @[], and @"" literals are hard-coded into Clang. You can see it here: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/AST/NSAPI.cpp?view=markup It's all fairly modular, meaning that it wouldn't be hard for a Clang hacker to add her own literal syntax... but "modular" doesn't mean "accessible from the outside". Adding a new syntax or even redirecting the existing syntax to new classes would definitely require rebuilding Clang yourself.

Here's a blog post about adding NSURL literals to Clang by hacking on its internals: http://www.stuartcarnie.com/2012/06/llvm-clang-hacking-part-3.html (Thanks @Josh Caswell)

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If you're willing to use Objective-C++ with C++11 extensions, you can has "user-defined literals", which allow you to write things like

NSURL *operator ""URL (const char *s) { return [NSURL URLWithString: @(s)]; }

int main() {
    ...
    NSURL *myurl = "ftp://foo"URL;
    ...
}

This was mentioned in the comments on Mike Ash's blog. http://www.mikeash.com/pyblog/friday-qa-2012-06-22-objective-c-literals.html But this doesn't look very Objective-C-ish (or very C++ish!), and it works only with an Objective-C++11 compiler, and in general please don't do this. :)