Extended Type Design.

[Sean Kelly]

Frits van Bommel wrote:
> 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.

So *that's* why Win32 doesn't complain when constant data is modified 
and pretty much every other OS does.  Good to know.

By the way... I feel the same about the meaning of 'const'.  On some 
level I still even think that const-by-default is the correct choice, 
but now that D has hit 1.0 that will be a much harder sell.


Sean