On 08/15/2015 04:45 AM, cym13 wrote:
> On Saturday, 15 August 2015 at 11:34:01 UTC, cym13 wrote:
>> On Saturday, 15 August 2015 at 11:25:20 UTC, vladde wrote:
>>> I made a PR to phobos where I modified `std.format.format`.
>>> https://github.com/D-Programming-Language/phobos/pull/3528
>>>
>>> However the auto builder fails, with the error message:
>>>> runnable/test23.d(1219): Error: cannot implicitly convert expression
>>>> (format("s = %s", s)) of type char[] to string
>>>
>>> The line which fails is `p = std.string.format("s = %s", s);`
>>>
>>> I don't understand why I can't convert a char[] to string.
>>
>> I think it has to do with the fact that string is an alias to
>> immutable(char)[] and you can't implicitely cast an immutable to a
>> regular variable.
That's actually correct (for reference types). As long as there is no
indirection, a value type can be casted implicitly:
struct S
{
int i;
}
void main()
{
auto i = immutable(S)();
auto m = S();
m = i; // copied; fine
}
> I phrased it completely wrong, an example will be better :
>
> import std.stdio;
>
> void fun(immutable(int)[] i) {
> i.writeln();
> }
>
> void main() {
> int[] i = [42];
> fun(i);
> }
>
> Will not compile because there is no certainty that fun() won't
> change the array
Actually, that's the job of 'const'. Here, it is not fun's ability to
mutate but the caller's. 'immutable' on a function interface means a
requirement: The caller *must* provide immutable data so that the
function can rely on it not being changed by anyone.
Ali
