writeln if not empty

[Timothee Cour]

Thanks! your solution is more robust (minus some caveats i mentioned) and
also trivially extends to variadics.


On Tue, Mar 11, 2014 at 2:07 PM, monarch_dodra <monarchdodra at gmail.com>wrote:

> On Tuesday, 11 March 2014 at 05:37:25 UTC, Timothee Cour wrote:
>
>> void writelnIfNotEmpty(T)(T a){
>> auto file_pos=get_filepos(stdin);
>> write(a);
>> if(get_filepos(stdin)!=file_pos)
>> writeln;
>> }
>>
>
> You could simply create an sink that forwards to stdout, while keeping
> state:
>
> //----
> import std.stdio, std.format;
>
> bool writelnIfNotEmpty(T)(T a)
> {
>     bool written = false;
>     void checkWriter(in char[] s)
>     {
>         if (s.length)
>         {
>             written = true;
>             write(s);
>         }
>     }
>     formattedWrite(&checkWriter, "%s", a);
>     if (written)
>     {
>         writeln();
>         return true;
>     }
>     return false;
> }
>
> void main()
> {
>     writelnIfNotEmpty(1);
>     writelnIfNotEmpty("");
>     writelnIfNotEmpty(2);
> }
> //----
>
> This prints:
> //----
> 1
> 2
> //----
>
> Also, this didn't work up until a few releases ago. I am really really
> happy to see code like this finally "just work". yay!
>
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