/static_antics

Fun with "P2741: user-generated static_assert messages"

Primary LanguageC++MIT LicenseMIT

static_antics

Fun with "P2741: user-generated static_assert messages"

Installation:

Why is P2741 special

P2741 adds a fantastic new feature to C++. Instead of being limited to static_asserts of the form

static_assert(false, "This has to be an _unevaluated_ literal");

we can now get away with silliness such as

static_assert(false, fmt::format("This can be {}", "whatever I want!"));

This opens the door to using static_assert messages as procedural output, which in turn means we can implement programs that take user input, do some computation, and then print out output to stderr from static_assert formatted output.

Wordle

Usage:

clang static_wordle.cpp -std=c++2c -Wno-everything -fconstexpr-steps=10000000 -DGUESS="CRANE HOUSE ETC"

#embed

Check if GCC supports embed yet here: https://godbolt.org/z/5hKx3Kz1a

With the advent of C23's #embed feature, we can now take user input at compile-time not just from preprocessor defines, but also from file input! That opens the door to a bunch more programs we can implement:

cat

Godbolt: https://compiler-explorer.com/z/EzEY6Tse9

Usage:

clang static_cat.cpp -std=c++2c -Wno-everything -fconstexpr-steps=10000000 -DCAT_FILE="path/to/file"

grep

Godbolt: https://compiler-explorer.com/z/jTdE13P4z

Usage:

clang static_grep.cpp -std=c++2c -Wno-everything -fconstexpr-steps=10000000 -DGREP_FILE="path/to/file" -DGREP_PATTERN="regex.*to.*match"

llama

Usage:

clang static_llama.cpp -std=c++2c -Wno-everything -fconstexpr-steps=10000000 -DPROMPT="Once upon a time, there was a C compiler named clang"

Yes, we can actually perform LLM inference inside of a single static_assert(false) now.

Pretty colors

Out of curiosity, I tried playing with some ANSI escape codes in the static_assert output. Unfortunately, I was thwarted by clang, who smartly recognized that it would be too fun if I could use those as well.

But GCC on the other hand...

TODO: Insert image

So... we can now do a few more completely wack things. If you compile Wordle using GCC14, you'll get pixel-perfect output to the official game:

TODO: Insert image

If you compile cat using GCC14 on an image, you'll get the image printed out using Kitty image protocol:

TODO: Insert image

If you compile grep using GCC14, you'll get colored text for matches:

TODO: Insert image