3 ms·

What is the argument in favor of specifically allowing casting away const of pointers?

• ridiculous_fish 10y ago
  The strongest argument is to support a sort of poor man's const-generics. Consider a function like strchr(). This locates a character in a (const) string, and returns a (non-const) pointer to it. The idea is that you can use this on both const and non-const strings. Call it on a const string, you get back a non-const pointer (which you better treat as const!) But call it on a non-const string, you get back a non-const pointer, with which you can mutate the string. So a single function serves both const and non-const uses. If casting away const-ness were disallowed, the compiler might conclude that strchr()'s returned value cannot alias the input string, and its optimizations would defeat this design. Anyways that's the original rationale.
  • mannykannot 10y ago
    It does not strike me as much of a benefit, and certainly not worth the cost of creating confusing semantics (in fact, I would prefer (a true) const to be the default in any language, with something like 'mutable' required to override.)
  • nialv7 10y ago
    And that's why D has the 'inout' qualifier
• WalterBright 10y ago
  Logical const and expressiveness.
• Rexxar 10y ago
  - In some case implementing both "const" and "non const" methods cause a lot of code duplications and cast can help. - Compatibility with old libraries
  • WalterBright 10y ago
    > implementing both "const" and "non const" methods cause a lot of code duplications D has an `inout` qualifier that has the effect of "transmitting" the const-ness of an argument to the return type.