nanbox

https://github.com/philihp/nanbox You don't even need a Double, you can use a Float NaN to encode strings: > IEEE 754 encodes 32-bit floating points with 1 bit for the sign, 8 bits for the exponent, and 23 bits for the number part (mantissa). (...) > 23 bits isn't much space, but conveniently the max size of a Unicode codepoint is 0x10FFFF, making it a 22-bit charset. When you encode your strings in UTF-32, you're only going to be using 22 of those bits, so masking the top portion with the NaN signature makes all of your characters NaNs.

It’s much more interesting to use the mantissa bits to store data than using a NaN as a very big bit. From nanbox [0] README: > IEEE 754 encodes 32-bit floating points with 1 bit for the sign, 8 bits for the exponent, and 23 bits for the number part (mantissa). For the specific case of NaN (e.g. the result of dividing 0 by 0, or the square root of a negative number), the spec encodes this as 11111111 in the exponent. The sign and the mantissa can be anything, and the spec suggests this can be used for "diagnostic information". One/some of these bits is/are commonly used to indicate a quiet NaN (qNaN) which could be expected vs. a signaling NaN (sNaN) which could be unexpected and should trigger an halting exception. This behavior is however sometimes different on different hardware. > 23 bits isn't much space, but conveniently the max siz