There is a bug here:

import std.stdio;

void main()
{
    int index;
    writef("The index is", index);
}

Actually I found this bug in some example code: http://d.puremagic.com/issues/show_bug.cgi?id=5836

writef is missing a format specifier. But it still accepts this code.

Is it possible for writef to statically check whether there's a format specifier, assuming there's multiple arguments and the first argument is a string literal?

I realize runtime checks would be out of the question, but I'm looking for compile-time checks when it's possible to do so.

Andrej Mitrovic:

> I realize runtime checks would be out of the question, but I'm looking for compile-time checks when it's possible to do so.

GCC is often able to catch such bugs, but Walter has recently closed my enhancement request about this :-( http://d.puremagic.com/issues/show_bug.cgi?id=4458

So a solution is to build a fwrite/fwriteln that uses a compile-time string for formatting, that performs compile-time tests using the more efficient CTFE of DMD 2.053:

int foo, bar;
fwriteln!"%d %s"(foo, bar); // compile-time error: bar isn't a string!

Bye,
bearophile

%s doesn't stand for string in D.

My issue is that the arguments don't get printed out due to missing specifiers. That is clearly a bug. But maybe it's not a huge bug since it's just printing that is involved.

Andrej Mitrovic Wrote:

> %s doesn't stand for string in D.

Yes it does.

> My issue is that the arguments don't get printed out due to missing specifiers. That is clearly a bug. But maybe it's not a huge bug since it's just printing that is involved.

I think it should do what it use to do which print the extra data at the end, or it should throw an exception.

bearophile Wrote:

> So a solution is to build a fwrite/fwriteln that uses a compile-time string for formatting, that performs compile-time tests using the more efficient CTFE of DMD 2.053:
> 
> int foo, bar;
> fwriteln!"%d %s"(foo, bar); // compile-time error: bar isn't a string!

Two complaints:

fprintf? A leading f is for file.
%s means format as a string not the type is a string.

> Bye,
> bearophile

On 4/12/11, Jesse Phillips <jessekphillips+D@gmail.com> wrote:
> Andrej Mitrovic Wrote:
>
>> %s doesn't stand for string in D.
>
> Yes it does.

I was quoting bearophile's "it should error" post, you know that.

Jesse Phillips:

> Two complaints:
> 
> fprintf? A leading f is for file.
> %s means format as a string not the type is a string.

Sorry, you are right, I am silly.

Bye,
bearophile

On Tue, 12 Apr 2011 01:55:24 +0200, Andrej Mitrovic wrote:

> On 4/12/11, Jesse Phillips <jessekphillips+D@gmail.com> wrote:
>> Andrej Mitrovic Wrote:
>>
>>> %s doesn't stand for string in D.
>>
>> Yes it does.
> 
> I was quoting bearophile's "it should error" post, you know that.

I do now. Though it still stands for string ;)

On 4/12/11, Jesse Phillips <jessekphillips+d@gmail.com> wrote:
> On Tue, 12 Apr 2011 01:55:24 +0200, Andrej Mitrovic wrote:
>
>> On 4/12/11, Jesse Phillips <jessekphillips+D@gmail.com> wrote:
>>> Andrej Mitrovic Wrote:
>>>
>>>> %s doesn't stand for string in D.
>>>
>>> Yes it does.
>>
>> I was quoting bearophile's "it should error" post, you know that.
>
> I do now. Though it still stands for string ;)
>

It still kicks printf's butt for not having to worry about writing all the right specifiers. Just put in %s and life's easy. :)

On Mon, 11 Apr 2011 16:35:39 -0400, Andrej Mitrovic <none@none.none> wrote:

> There is a bug here:
>
> import std.stdio;
>
> void main()
> {
>     int index;
>     writef("The index is", index);
> }
>
> Actually I found this bug in some example code: http://d.puremagic.com/issues/show_bug.cgi?id=5836
>
> writef is missing a format specifier. But it still accepts this code.
>
> Is it possible for writef to statically check whether there's a format specifier, assuming there's multiple arguments and the first argument is a string literal?
>
> I realize runtime checks would be out of the question, but I'm looking for compile-time checks when it's possible to do so.

Why would runtime checks be out of the question?  You are already parsing the string at runtime, why can't it say "hey, I processed the whole format string, but I have these arguments left over"?  Would be a simple if statement...

A compile-time check would be nice, but you'd have to pass it as a compile-time argument (i.e. a template parameter), which would be not-so-nice.

What would be nice is if the compiler could check when you give it a string literal, and resort to runtime checks when it was a variable.   I don't think that's possible, however.

-Steve