• Mafi (30/30) Apr 23 2017 Hi there,
• =?UTF-8?Q?Ali_=c3=87ehreli?= (11/13) Apr 23 2017 Appender recommended:
• Mafi (13/27) Apr 23 2017 Thank you. I see. But I would really like not to allocate ever.
• Jonathan Marler (10/15) Apr 23 2017 Use sformat:

Mafi <mafi example.org> writes:

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)

=?UTF-8?Q?Ali_=c3=87ehreli?= <acehreli yahoo.com> writes:

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

Mafi <mafi example.org> writes:

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.

Jonathan Marler <johnnymarler gmail.com> writes:

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.