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.

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.

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.

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 while the following will work

    import std.stdio;

    void fun(immutable(int)[] i) {
        i.writeln();
    }

    void main() {
        int[] i = [42];
        fun(i.dup);

        immutable(int)[] j = [42];
        fun(j);

        immutable(int[]) k = [42];
        fun(k);
    }

On 08/15/2015 01:25 PM, 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.

Get rid of the 'in' in format's signature.

On 08/15/2015 01:54 PM, Timon Gehr wrote:
> On 08/15/2015 01:25 PM, 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.
>
> Get rid of the 'in' in format's signature.

Oh, I see, this is by design (which I don't like, but OK.)
The reason the conversion does not go through is that format is not marked as pure.

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