Re: print function
On Friday, 5 February 2016 at 12:35:14 UTC, Artur Skawina wrote:
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
Oh wow, and you thought to actually test it. I was just
eyeballing the code and running my mouth off. I can't fathom how
that's possible, because the only thing the write() template does
is translate each string argument to put(w,arg) where w is a
LockingTextWriter, and LockingTextWriter.put only outputs a
string if the sizeof... oh.
Yeah, my bad. Now I see it only puts each character as a string,
one at a time, if those characters are wide characters or
multibyte characters. It only does that if C.sizeof!=1 and I was
confusing .sizeof for .length. So for w"abc" it would put "a\0"
"b\0" "c\0" three times, I think, but for just "abc" it goes
straight to fwrite. It's the length of each character in bytes,
not the length of each string.
utf-8 encoded is still C.sizeof==1 I'm pretty sure. It's only
when you try to decode the characters or make "ropes" that you
end up with that iterative expansion of put().
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.
Maybe you should look again? I thought it was rather elegant,
except for the bizarre individual-character expansion that I
mistook for reality. It's not fast, but... very safe. Any D
process is going to lock the specific area of the file, so that
when you read a bunch, you're not going to have it change halfway
through, and two things aren't going to be writing in the same
place at the same time, at least not within individual write
calls.
Re: print function
On Friday, 5 February 2016 at 07:04:27 UTC, cy wrote:
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");
Up to here, yes.
And presumably, write() unrolls its arguments too. Each string
argument to write() unrolls to a put(). And put("abc") unrolls
into put("a");put("b");put("c"), each of which that call the C
routine fwrite with a length 1.
No, (explicit) unrolling with foreach could only happen if
there's either a variadic argument list, or if "abc" were a
template argument. (In the latter case you'd need more than a
simple foreach.) Of course, I don't know whether put() call
fwrite() for every single character (these are written with
single quotes, btw), but that wouldn't be unrolling strictu sensu.
Re: print function
On Thursday, 4 February 2016 at 22:13:36 UTC, Ola Fosheim Grøstad wrote: Well, it is probably not the best point in time to have absolute beginners use D anyway. That is a ridiculous thing to say and a great way of ensuring a language dies. Good starting resources help everyone.
Re: print function
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
Re: print function
On Friday, 5 February 2016 at 12:35:14 UTC, Artur Skawina wrote: 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. What do you use instead? A buffer and Posix write() and aio_write()?
Re: print function
On Friday, 5 February 2016 at 07:04:27 UTC, cy wrote: tl;dr speed demons use std.stream.InputStream.read() whenever you can, and std.stream.OutputStream.write() its result. Isn't std.stream deprecated?
Re: print function
On 02/05/16 14:38, Ola Fosheim Grøstad via Digitalmars-d-learn wrote:
> On Friday, 5 February 2016 at 12:35:14 UTC, Artur Skawina wrote:
>> 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.
>
> What do you use instead? A buffer and Posix write() and aio_write()?
For ad-hoc temporary debugging usually a local wrapper
@noinline writeln(A...)(A a) {
import std.stdio;
std.stdio.writeln(a);
}
[the reason for @noinline is to not disturb the caller]
This is where the `print` function would be useful. It
could even be made to work at CT (w/ compiler help; this
has been a often requested feature).
For programs that output one or few text lines to stdout
(results, status updates etc) - `printf` -- it's already
there in libc anyway, so zero-cost and GC-free.
For everything else - the C/Posix functions.
artur
Re: print function
On Thursday, 4 February 2016 at 10:18:35 UTC, ixid wrote: Do you think your knowledge and experience is a good model for how a new user who hasn't done much if any programming before would approach this? A design choice had to be made and made it was. Adding another function now (or worse, changing the existing ones) would only bring more confusion for beginners and unconsistency to the language. I firmly believe that no matter what your experience you have having one and preferably only one way to do things is more important to ease the learning process than having spaces or not.
Re: print function
On Thursday, 4 February 2016 at 10:59:50 UTC, Mike Parker wrote: IMO, while giving beginner's a helping hand is a great thing, I don't think it's a good basis to use as a design for a standard library. Yes, better to have a "beginners toolkit" starting-point-codebase and build a tutorial around it.
Re: print function
On Thursday, 4 February 2016 at 11:04:23 UTC, cym13 wrote: On Thursday, 4 February 2016 at 10:18:35 UTC, ixid wrote: Do you think your knowledge and experience is a good model for how a new user who hasn't done much if any programming before would approach this? A design choice had to be made and made it was. Adding another function now (or worse, changing the existing ones) would only bring more confusion for beginners and unconsistency to the language. I firmly believe that no matter what your experience you have having one and preferably only one way to do things is more important to ease the learning process than having spaces or not. That's a nonsensical argument given the number of printing and writing functions that exist.
Re: print function
On Thursday, February 04, 2016 00:40:55 ixid via Digitalmars-d-learn wrote:
> On Thursday, 4 February 2016 at 00:30:03 UTC, cym13 wrote:
> > On Thursday, 4 February 2016 at 00:23:07 UTC, ixid wrote:
> >> It would be nice to have a simple writeln that adds spaces
> >> automatically like Python's 'print' in std.stdio, perhaps
> >> called print.
> >
> > Sounds way too redundant to me.
>
> Normally you'd be right but printing out data is such a common
> thing, especially for beginners. It's the kind of thing that can
> make their early experience of a language a lot more positive.
>
> writeln(a, " ", b, " ", c, " ", d);
>
> Is very clunky. Programming languages are like cereal, you need
> sugar to get the kids hooked.
I would normally expect someone to do that with writefln, which would be
cleaner. e.g.
writefln("%s %s %s %s", a, b, c, d);
Personally, I've never felt the need for a function like you're describing.
- Jonathan M Davis
Re: print function
On Thursday, 4 February 2016 at 10:18:35 UTC, ixid wrote:
On Thursday, 4 February 2016 at 10:05:15 UTC, Jonathan M Davis
wrote:
I would normally expect someone to do that with writefln,
which would be cleaner. e.g.
writefln("%s %s %s %s", a, b, c, d);
Personally, I've never felt the need for a function like
you're describing.
- Jonathan M Davis
Do you think your knowledge and experience is a good model for
how a new user who hasn't done much if any programming before
would approach this?
IMO, while giving beginner's a helping hand is a great thing, I
don't think it's a good basis to use as a design for a standard
library.
Re: print function
On Thursday, 4 February 2016 at 10:05:15 UTC, Jonathan M Davis
wrote:
I would normally expect someone to do that with writefln, which
would be cleaner. e.g.
writefln("%s %s %s %s", a, b, c, d);
Personally, I've never felt the need for a function like you're
describing.
- Jonathan M Davis
Do you think your knowledge and experience is a good model for
how a new user who hasn't done much if any programming before
would approach this?
Re: print function
On Thursday, 4 February 2016 at 14:25:21 UTC, bachmeier wrote: Unfortunately there is no such thing and it is unlikely to exist in the next decade. Well, it is probably not the best point in time to have absolute beginners use D anyway. But a well commented library, that don't focus on performance and teach good habits using the non-advanced D feature subset, can go a long way if the design is explained in a companion tutorial. A "build your own pythonesque library" tutorial wrapped up as a zip-file with a sensible main-file template that is ready to compile. That way newbies can just unzip it into a new directory when they start a new project "resetting" former mistakes.
Re: print function
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");
And presumably, write() unrolls its arguments too. Each string
argument to write() unrolls to a put(). And put("abc") unrolls
into put("a");put("b");put("c"), each of which that call the C
routine fwrite with a length 1.
So the above print, if you did print("hi","there") it would become
write("hi"," "); write("there","\n")
which would become
put("hi");put(" ");put("there");put("\n");
which would become
put("h");put("i");put("
");put("t");put("h");put("e");put("r");put("e");put("\n");
And then it compiles.
Any literal string you pass to std.stdio.write will be expanded
into 1 fwrite invocation per character. And
std.format.formattedWrite is called on aggregate types like
lists, which stringifies each value, and passes the string to
put(), resulting in again, 1 fwrite per character.
Why put() doesn't just call fwrite without expanding into 1
character strings, I have no idea. Something with wide
characters, I guess? But even then it could use one fwrite for
normal characters. It's not like
fwrite("a",1,1,stdout);fwrite("b",1,1,stdout);
will fail any less if the output stream dies before "b" than
fwrite("ab",2,1,stdout);
Why put() doesn't call the C "fputc" function for 1 character
strings, I *really* have no idea.
Seems to me some fancy code generation producing write("a"," ",
"b", " ", "c", "\n") or even put("a b c\n") would still expand
into 1 put() per character, before it finished compiling.
tl;dr speed demons use std.stream.InputStream.read() whenever you
can, and std.stream.OutputStream.write() its result. Don't expect
std.stdio to let you have nice things. std.file.write is always
preferable if you can generate the whole file beforehand.
Re: print function
On Thursday, 4 February 2016 at 11:04:15 UTC, Ola Fosheim Grøstad
wrote:
On Thursday, 4 February 2016 at 10:59:50 UTC, Mike Parker wrote:
IMO, while giving beginner's a helping hand is a great thing,
I don't think it's a good basis to use as a design for a
standard library.
Yes, better to have a "beginners toolkit"
starting-point-codebase and build a tutorial around it.
That would be a reasonable argument if such a thing existed and
was included with the compiler.
import newbie;
void main() {
print("Jack", "Black");
}
Unfortunately there is no such thing and it is unlikely to exist
in the next decade.
Re: print function
On Thursday, 4 February 2016 at 14:25:21 UTC, bachmeier wrote: Unfortunately there is no such thing and it is unlikely to exist in the next decade. There is http://forum.dlang.org/post/mtsd38$16ub$1...@digitalmars.com
Re: print function
On Thursday, 4 February 2016 at 00:23:07 UTC, ixid wrote: It would be nice to have a simple writeln that adds spaces automatically like Python's 'print' in std.stdio, perhaps called print. There are many implementations of string interpolation in D (that is what you want, basically). One of them is given in Phillipe's excellent book about templates: https://github.com/PhilippeSigaud/D-templates-tutorial/blob/master/D-templates-tutorial.md#simple-string-interpolation .
Re: print function
On Thursday, 4 February 2016 at 13:46:46 UTC, Dejan Lekic wrote:
On Thursday, 4 February 2016 at 00:23:07 UTC, ixid wrote:
It would be nice to have a simple writeln that adds spaces
automatically like Python's 'print' in std.stdio, perhaps
called print.
There are many implementations of string interpolation in D
(that is what you want, basically). One of them is given in
Phillipe's excellent book about templates:
https://github.com/PhilippeSigaud/D-templates-tutorial/blob/master/D-templates-tutorial.md#simple-string-interpolation .
I have written an attempt at it but my point was that a print
function would be a good addition to the standard library rather
than asking someone to write an implementation for me.
string makePrintString(T)(T length) {
import std.conv : to;
string s = "writeln(";
foreach( i; 0 .. length) {
s ~= "a[" ~ i.to!string ~ "]";
if(i != length - 1)
s ~= ",\" \",";
else s ~= ");";
}
return s;
}
void print(A...)(A a) {
static if(a.length) {
mixin(makePrintString(a.length));
} else writeln;
}
Re: print function
On 02/04/16 15:02, ixid via Digitalmars-d-learn wrote:
> On Thursday, 4 February 2016 at 13:46:46 UTC, Dejan Lekic wrote:
>> On Thursday, 4 February 2016 at 00:23:07 UTC, ixid wrote:
>>> It would be nice to have a simple writeln that adds spaces automatically
>>> like Python's 'print' in std.stdio, perhaps called print.
> I have written an attempt at it but my point was that a print function would
> be a good addition to the standard library rather than asking someone to
> write an implementation for me.
>
> string makePrintString(T)(T length) {
> import std.conv : to;
>
> string s = "writeln(";
> foreach( i; 0 .. length) {
> s ~= "a[" ~ i.to!string ~ "]";
> if(i != length - 1)
> s ~= ",\" \",";
> else s ~= ");";
> }
>
> return s;
> }
>
> void print(A...)(A a) {
> static if(a.length) {
> mixin(makePrintString(a.length));
> } else writeln;
> }
void print(A...)(A a) {
foreach (N, ref e; a)
write(e, N==A.length-1?"\n":" ");
}
artur
Re: print function
On Thursday, 4 February 2016 at 15:10:18 UTC, Kagamin wrote: On Thursday, 4 February 2016 at 14:25:21 UTC, bachmeier wrote: Unfortunately there is no such thing and it is unlikely to exist in the next decade. There is http://forum.dlang.org/post/mtsd38$16ub$1...@digitalmars.com The important feature is the one that it doesn't offer - it's not part of the default installation. Without that, it doesn't help new users much. It's not even listed on the "Getting Started" for that matter.
Re: print function
On Thursday, 4 February 2016 at 00:23:07 UTC, ixid wrote: It would be nice to have a simple writeln that adds spaces automatically like Python's 'print' in std.stdio, perhaps called print. It seems Andrei decided to add such function: http://forum.dlang.org/thread/n8vr0l$ist$1...@digitalmars.com
Re: print function
On 02/04/16 16:32, Artur Skawina wrote:
>
>void print(A...)(A a) {
> foreach (N, ref e; a)
> write(e, N==A.length-1?"\n":" ");
>}
BTW, that was *deliberately* written that way as a compromise
between efficiency and template bloat. It can of course be
done like
void print(alias SEP=" ", alias EOL="\n", A...)(A a) {
mixin(`write(`~iota(A.length).map!(a=>"a["~text(a)~"],")().join("SEP,")~"EOL);");
}
but that seems too expensive, when the use is just in toy
programs and debugging.
artur
Re: print function
On Thursday, 4 February 2016 at 17:34:33 UTC, Artur Skawina wrote: On 02/04/16 16:32, Artur Skawina wrote: but that seems too expensive, when the use is just in toy programs and debugging. I hadn't really considered the relative cost-benefit, it's just a habit to try to hardcode things at compile time. =) It certainly seems to make sense to do it that way.
Re: print function
On 02/04/16 18:53, ixid via Digitalmars-d-learn wrote: > On Thursday, 4 February 2016 at 17:34:33 UTC, Artur Skawina wrote: >> On 02/04/16 16:32, Artur Skawina wrote: >> but that seems too expensive, when the use is just in toy programs and >> debugging. > > I hadn't really considered the relative cost-benefit, it's just a habit to > try to hardcode things at compile time. =) It certainly seems to make sense > to do it that way. Just to clarify -- *all* versions work at CT; the static-foreach will be unrolled at CT, and the mixin argument will be fully evaluated at CT too. The only difference is in a) readability, b) the `write` template instantiations (and potential re-use). Using the std lib `write*` templates has a huge cost; for any kind of /real/ programs, that care about performance at all, they are better avoided. (But it probably doesn't matter if you already heavily rely on GC and don't print much, other than that they add tons of code to the executable) artur
Re: print function
On Thursday, 4 February 2016 at 00:30:03 UTC, cym13 wrote: On Thursday, 4 February 2016 at 00:23:07 UTC, ixid wrote: It would be nice to have a simple writeln that adds spaces automatically like Python's 'print' in std.stdio, perhaps called print. Sounds way too redundant to me. Normally you'd be right but printing out data is such a common thing, especially for beginners. It's the kind of thing that can make their early experience of a language a lot more positive. writeln(a, " ", b, " ", c, " ", d); Is very clunky. Programming languages are like cereal, you need sugar to get the kids hooked.
Re: print function
On Thursday, 4 February 2016 at 00:23:07 UTC, ixid wrote: It would be nice to have a simple writeln that adds spaces automatically like Python's 'print' in std.stdio, perhaps called print. Sounds way too redundant to me.
Re: print function
On Thursday, February 04, 2016 00:23:07 ixid via Digitalmars-d-learn wrote: > It would be nice to have a simple writeln that adds spaces > automatically like Python's 'print' in std.stdio, perhaps called > print. If that's what you're looking for, I expect that most of us would think that it's just better to use writefln with a format string. But if you really want it, you can always create such a wrapper yourself. - Jonathan M Davis
