double y = 0.0; // initialized to 0.0
double x; // initialized to NaN
I don't know of any other programming language with this safety feature.
Also, the D `char` type is initialized to 0xFF, not 0, because Unicode says that 0xFF is an invalid character.
The trouble with it is a bug I've seen often. People will get an error message about an "uninitialized variable". Then they go into "just get the compiler to shut up" mode, amd pick "0" as the initializer. Then, the program compiles and runs, and silently produces the wrong answer. Code reviews will simply pass over the "0" initializer, as it looks right.
With default NaN initialization, the programmer is more likely to stop and think about it, not just insert 0.
Another issue with it is:
float x = 0.0;
setFloat(&x);
void setFloat(float* px) { *px = 3.0; }
But I contend it's more useful (and interesting) to think about the idea with your own mind instead of tallying up the perceived authority of its supporters and relying on trust. It was also somewhat rude to suggest that the OP had not given their idea much thought. This is a forum for discussion, isn't it?
Like not allowing macros in D, or version algebra.
Not so. You may be thinking of UTF-8 encoding. 0xff is DEL in Unicode.
For me, the major advantage of nan boxing is that you don't have to allocate a whole class of types (like floats). That saves so much at garbage collection time.
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[1] https://en.wikipedia.org/wiki/Hilbert%27s_paradox_of_the_Gra...