Unofficial wish list status.(Jul 2008)

[Steven Schveighoffer]

"Jason House" wrote
> Steven Schveighoffer Wrote:
>
>> >> They don't make any less sense than declaring invariant variables.  Or
>> >> declaring invariant parameters.
>> >>
>> >> Can you see use in the following function signature:
>> >>
>> >> void f(invariant(somestruct) *x) {...}
>> >>
>> >> If so, an invariant member function is no different.
>> >
>> > Will the fields of somestruct be accessed directly?  If so, there's no
>> > change in functionality.  If not, will the invariant functions of
>> > somestruct be used to modify global state?  If not, there's not change 
>> > in
>> > functionality...  I don't think what I'm suggesting changes a lot of 
>> > code.
>>
>> You are suggesting that invariant functions simply be illegal, and pure
>> functions not.  I am saying that you are leaving a hole in the type 
>> system
>> by doing that.  It is analogous to saying, if a function has any 
>> invariant
>> parameters, those functions should be marked pure, and all parameters 
>> should
>> be marked invariant.  I can see many places where some parameters could 
>> be
>> invariant and some not.  Pure functions (as Walter envisions them) 
>> require
>> ALL invariant parameters.
>
>
> No, I'm not.  I'm only suggesting that functions that are invariant and 
> const functions are redefined to be like pure functions...  Merging 
> concepts together.  There's no reason for an invariant argument to a 
> function require the function itself to be invariant/pure.

An invariant function is defined as one that has an invariant argument (the 
'this' pointer).  There are no other special requirements for invariant 
functions.  So I think you still don't understand the concept.

invariant functions === invariant data.

-Steve