Extended Type Design.

[Frits van Bommel]

Walter Bright wrote:
> Frits van Bommel wrote:
>> Seriously though:
>> "readonly" would mean that you (meaning any code that can access the 
>> symbol so declared) can only read data referenced through it, but 
>> someone else _may_ be able to write to it[2].
> 
> My perception of that is different. I used to do embedded systems, and
> 'readonly' means the data went into ROM. Also, marking a page in a 
> virtual memory system as 'readonly' means that nobody can modify it.

Perhaps, but my perception of 'const' is different ;). Particularly, it 
seems to be short for "constant", which is therefore what it should 
mean. Not "*you* can't change this, but someone else might anyway".

Oh, and on x86 (and amd64) processors the operating system is allowed to 
write to 'readonly'[1] pages unless it sets the WP (Write-Protect) bit 
in system register CR0. Note: as this bit is *off* by default, it needs 
to be explicitly turned on by the OS.


[1] Well, technically they're not really readonly, it's more like 
non-writable (since the appropriate bit must be 1 on all levels of the 
paging data structures to get a writable page) but that's heading /even 
faster/ into the realm of nitpicking :).


> 'super const' at least has the connotation of being "constant, this time 
> we mean it".

Wouldn't it be better if 'const' just _meant what it said_ in the first 
place? :P