const

[Don Clugston]

Walter Bright wrote:
> Don Clugston wrote:
>> Ditto. Come on, even non-programmers know what "read only access" means.
>> I find it hard to believe there would be many people who'd have 
>> trouble grasping the idea that "read only" means "look but don't 
>> touch". Are there any languages where 'readonly' is used for putting 
>> values into ROM?
> 
> Yes, there are C extensions to do just that. Secondly, there is often 
> hardware memory protection available, which has a "read only" bit. That 
> means the data cannot be changed.

It's pretty common for the OS to load the exe into writable memory, then set the 
readonly bit. "read only" = the OS can write to it, but you can only read it.
Ditto for files -- the administrator can always delete them.

  Files marked "read only" cannot be
> written to by anyone. Read only has a long history of meaning immutable 
> by anything, not just the viewer.
> 
> "The readonly storage-class modifier, like the const data-type 
> qualifier, assigns the NOWRT attribute to the variable's program 
> section; if used with the static or globaldef specifier, the variable is 
> stored in the $CODE psect, which has the NOWRT attribute by default." -- 
> http://h71000.www7.hp.com/commercial/c/docs/5492profile_017.html
> 

That looks pretty obscure to me. Besides, a paragraph later, that page describes 
const and readonly as pretty much synonymous:

"For new program development, HP recommends that you use the const  modifier, 
because const  is standard-conforming and readonly  is not."

How often have you heard someone say "sorry, I only have read-only access to 
that directory?"