Const sucks

[Walter Bright]

Russell Lewis wrote:
> Walter Bright wrote:
>> What we are trying to achieve:
>>
>> a) utility for functional programming
>> b) better modularity by self-documenting interfaces better
>> c) be able to treat reference types as if they were value types (i.e. 
>> strings should behave to the user like value types, even though they 
>> are references)
> 
> Is there a way to express (for a pointer passed as a function parameter) 
> "the callee is allowed to modify this object through the pointer, but 
> the caller ensures that no other code will be modifying it at the same 
> time"?   Sort of a "you have exclusive write access" modifier?  Is that 
> a common enough case to even support?

That's sort of what the often proposed 'unique' type qualifier does. The 
problem is, there's just no reasonable way to implement it in a 
*checkable* manner. And if it ain't checkable, it's about as useful as 
painting a black stripe across your lap when driving instead of wearing 
a seatbelt.