On 11/30/2010 05:39 PM, Andrei Alexandrescu wrote:
On 11/30/10 5:25 AM, Max Samukha wrote:
On 11/30/2010 02:35 AM, Walter Bright wrote:
Fawzi Mohamed wrote:
logical const is useful for lazy functions and memoization, and if
implemented correctly it is perfectly safe.
As I said in an older discussions, to have it with the current system
all that is needed is some guarantees that the compiler will not
disallow "unsafe" changes (by moving to read only memory for
example)in some cases.
For example casted mutable types, so that casting to mutable works.
D allows escape from the type system, but the programmer who does that
loses the guarantees, and it's up to him to ensure that the result
works.
String literals, for example, are going to often wind up in read only
memory.
The problem is that logical const has many perfectly valid use cases.
You cannot simply tell people: "Don't use it. It is a fraud". They will
still be using casts or not using D. As casting away const is undefined
behavior in D, the outcome will be every second non-trivial D program
relying on undefined behavior.
I'm not seeing half of non-trivial C++ programs using mutable.
Andrei
That was a hyperbole. But logical const is obviously not some obscure
corner case. Objects with reference counters, proxy objects, objects
keeping access statistics (e.g. for debugging purposes), objects using
logger objects, etc - all require logical const. To corroborate, Qt
sources have over 600 'mutable' field declarations.
