Hi there,
every time I want to use output-ranges again they seem to be broken in a different way (e.g. value/reference semantics). This time it is char types and encoding.

How do I make formattedWrite work with a char buffer? I tried the following code and it fails with a *static assert*; it is itentionally disabled. I suspects it is again something about autodecoding but in this case I don't understand it.

https://dpaste.dzfl.pl/c68b3e3529f6

```
import std.format, std.stdio;

void main() {
	char[20] buffer;
	formattedWrite(buffer[], "Long string %s\n", "more more more");
	write(buffer);
}
```

Compilation output:

/opt/compilers/dmd2/include/std/range/primitives.d(351): Error: static assert  "Cannot put a char into a char[]."
/opt/compilers/dmd2/include/std/format.d(2647):        instantiated from here: put!(char[], char)
/opt/compilers/dmd2/include/std/format.d(2297):        instantiated from here: formatRange!(char[], string, char)
/opt/compilers/dmd2/include/std/format.d(3778):        instantiated from here: formatValue!(char[], string, char)
/opt/compilers/dmd2/include/std/format.d(460):        instantiated from here: formatGeneric!(char[], string, char)
/d446/f470.d(5):        instantiated from here: formattedWrite!(char[], char, string)

On 04/23/2017 04:17 AM, Mafi wrote:

> /opt/compilers/dmd2/include/std/range/primitives.d(351): Error: static
> assert  "Cannot put a char into a char[]."

Appender recommended:

import std.format, std.stdio, std.array;

void main() {
    auto sink = appender!(char[])();
    formattedWrite(sink, "Long string %s\n", "more more more");
    write(sink.data);
}

Of course appender!string is more natural but I just wanted to see that it works with char[] as well.

Ali

On Sunday, 23 April 2017 at 12:03:58 UTC, Ali Çehreli wrote:
> On 04/23/2017 04:17 AM, Mafi wrote:
>
>> /opt/compilers/dmd2/include/std/range/primitives.d(351): Error: static
>> assert  "Cannot put a char into a char[]."
>
> Appender recommended:
>
> import std.format, std.stdio, std.array;
>
> void main() {
>     auto sink = appender!(char[])();
>     formattedWrite(sink, "Long string %s\n", "more more more");
>     write(sink.data);
> }
>
> Of course appender!string is more natural but I just wanted to see that it works with char[] as well.
>
> Ali

Thank you. I see. But I would really like not to allocate ever. Instead I want to fill a given buffer, then stop formatting.

I probably have to implement my own output-range for this use case. It would fill the buffer and then ignore further 'put'-calls. I can live with this.

I do have a follow-up question though. Why does formattedWrite take the output-range by value? It just doesn't make sense for value-type output-ranges; especially with consecutive calls. One has to pass the pointer of the output-range (this does work because of auto-dereferencing). Forgetting it one place, lets the code still compile, with very strange semantics which most probably were not intended.

On Sunday, 23 April 2017 at 11:17:37 UTC, Mafi wrote:
> Hi there,
> every time I want to use output-ranges again they seem to be broken in a different way (e.g. value/reference semantics). This time it is char types and encoding.
>
> [...]

Use sformat:

import std.format, std.stdio;

void main() {
	char[20] buffer;
	sformat(buffer, "Long string %s\n", "more more more");
	write(buffer);
}

Note: the buffer is not large enough to hold the entire string in your example so this will cause a stack buffer overflow.