print function

[Artur Skawina via Digitalmars-d-learn]

On 02/05/16 08:04, cy via Digitalmars-d-learn wrote:
> On Thursday, 4 February 2016 at 15:32:48 UTC, Artur Skawina wrote:
>>    void print(A...)(A a) {
>>       foreach (N, ref e; a)
>>          write(e, N==A.length-1?"\n":" ");
>>    }
> 
>>> will be unrolled at compile time
> 
> Mind if I elaborate on this a bit? If that is unrolled, I understand it will unroll into several calls to write, as in print("1","2","3") => write("1"," ");write("2"," ");write("3","\n");

Yes, and they are all using the same `write!(string, string)` instance
(there will be one for every printed type, `write!(typeof(A[N]), string)`).


> Any literal string you pass to std.stdio.write will be expanded into 1 fwrite invocation per character.

D's std lib implementations are sometimes really awful, but in
this case it's not actually that bad:

   print("hi","there");

->

   fwrite("hi", 1, 2, 0x7ff68d0cb640)                         = 2
   fwrite(" ", 1, 1, 0x7ff68d0cb640)                          = 1
   fwrite("there", 1, 5, 0x7ff68d0cb640)                      = 5
   fwrite("\n", 1, 1, 0x7ff68d0cb640)                         = 1


What happens between `print` and `fwrite` - I have no idea.
Years ago I had to investigate why phobos showed up in the
perf profile of a program, when the only used part was some
`write` call used to print diagnostics. What I saw made me
never use or look at D's std lib again. Except for meta
programing and toy/example programs where it doesn't matter.

artur