Const foreach

[Simen kjaeraas]

spir <denis.spir at gmail.com> wrote:

> On Sun, 21 Nov 2010 20:21:14 -0500
> bearophile <bearophileHUGS at lycos.com> wrote:
>
>> If in a D2 program I have an array of mutable items I may want to  
>> iterate on them but not modify them, so I'd like the iteration variable  
>> to be const. This is possible, but it seems I lose type inference:
>>
>>
>> void main() {
>>     int[3] array; // not const
>>     // foreach (const x; array) {}                // Error
>>     // foreach (const auto x; array) {}           // Error
>>     // foreach (const(int) x; array) {}           // OK
>>     foreach (const(typeof(array[0])) x; array) {} // OK
>> }
>>
>>
>> Is something wrong in that code? Is this a known limitation, an  
>> inevitable one? Is this an enhancement request worth adding to Bugzilla?
>>
>> Bye and thank you,
>> bearophile
>
> Maybe you'll find it weird, but I would expect
>     foreach (const(auto) x; array) {};
> to be the logical idiom for this. "auto" beeing a kind of placeholder  
> for a type name.

'auto' is not a placeholder for a type, but the default storage class.
IOW, 'int n;' == 'auto int n;'. This does however not compile,
complaining that it has no effect.

Specifying just the storage class signals the compiler to use type
inference. Try it:

const x = 4;
immutable y = 4;

-- 
Simen