![[personal profile]](https://www.dreamwidth.org/img/silk/identity/user.png) simont |
Thu 2011-12-08 11:30 |
You can specify the const keyword when defining a class method, indicating that it's permissible to apply the method to a const instance of that class.
But the semantics aren't quite the same. It's easy to imagine functions that don't change any state and are safe to apply to a const object, but which nonetheless don't reliably return the same value if called twice. (For instance, a function that returns the number of nanoseconds until the object's expiry date, or one that returns the current contents of the file whose pathname is stored in the object. eta: or, come to think of it, a function that simply dereferences a pointer stored in the object! Much simpler, and no need to invoke the mysterious concurrency of the real world :-)
So you actually want a marker less like "const" and more like "pure", indicating that whatever the function does has no side effects and depends on only the obvious input values, so that the optimiser is permitted to assume that apparently identical calls to it are actually identical and fold them together. |
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