Efficient outputting of to-string conversions

[Steven Schveighoffer]

On Tue, 08 Feb 2011 11:09:44 -0500, Steven Schveighoffer  
<schveiguy at yahoo.com> wrote:

> On Tue, 08 Feb 2011 10:55:23 -0500, spir <denis.spir at gmail.com> wrote:
>
>> On 02/07/2011 11:38 PM, Tomek Sowiński wrote:
>>> Jonathan M Davis napisał:
>>>
>>>> On Monday 07 February 2011 13:10:09 Tomek Sowiński wrote:
>>>>> Looks like std.conv.to always allocates behind the scenes. It's a  
>>>>> shame as
>>>>> the returned string is immediately processed and discarded in my XML
>>>>> writer. Are there plans to include a custom output variant, e.g.
>>>>> to!string(7, outputRange)?
>>>>
>>>> http://prowiki.org/wiki4d/wiki.cgi?LanguageDevel/DIPs/DIP9
>>>
>>> I know about Steven's proposal but it applies only to user types not  
>>> primitives. Either way std.conv.to would need a buffered output range  
>>> as integers are written from the right. Any chance for an abstraction  
>>> analogous to buffered input ranges discussed recently?
>>
>> I haven't read a solution like the proposal for writeTo would not apply  
>> to primitives. Is it really so? (If only for language consistency, I  
>> would prefere this big shift to apply to all types.)
>
> writeTo does not need to apply to primitives because primitives can be  
> written to streams without first converting to char[].  For instance,  
> one does not write:
>
> writeln(to!string(5))
>
> The whole point of writeTo is to allow easy output of custom data types  
> that the standard library does not know how to output.  It was not meant  
> to extend to primitives.
>
> As far as Tomek's request, I would expect  
> std.format.formattedWrite(buffer, "%s", 7) to work, or  
> std.format.formatValue (with associated FormatSpec, which I don't feel  
> like looking up the usage of)

BTW, I think we probably should have a formatValue override like this

void formatValue(Char, Writer, T)(Writer w, T t)
{
    FormatSpec!Char fs; // use default options
    formatValue(w, t, fs);
}

Having to construct a FormatSpec when I just want the default seems like  
overkill.  Esp. since FormatSpec arg is always ref.

-Steve