On 07/09/2012 05:00 PM, H. S. Teoh wrote:
On Mon, Jul 09, 2012 at 01:44:24PM +0200, Timon Gehr wrote:
On 07/09/2012 08:37 AM, Adam Wilson wrote:
Object is now const-correct throughout D. This has been a dream for
many of you. Today it is a reality.
PITA. Forced const can severely harm a code base that wants to be
flexible -- it leaks implementation details and is infectuous.
[...]
Can you give an explicit example of code that is harmed by const
correctness?
1.
Most code that gives amortized complexity guarantees, eg:
interface Map(K, V){
V opIndex(K k) const;
// ...
}
class SplayTree(K, V) : Map!(K, V) {
// ???
}
2.
- hash table
- opApply compacts the table if it is occupied too sparsely, in order
to speed up further iteration.
- toString iterates over all key/value pairs by the means of opApply.
Clearly, toString cannot be const in this setup.
3.
Often, objects can cache derived properties to speed up the code. With
'const-correctness' in place, such an optimization is not transparent
nor doable in a modular way.
IME, it rather helps code quality than harm it.
I am not talking about code quality. I am talking about code
maintainability, extensibility and performance.
Besides, since everything converts to const, it doesn't harm as much code as one
might imagine (most code will be unchanged except where it matters --
which IMO is a good thing).
Methods do not convert to const.
