• Peter Sommerfeld (6/6) Mar 16 2013 Cannot find a reference: What is the best way
• 1100110 (3/9) Mar 16 2013 foreach(0..4)
• 1100110 (5/15) Mar 16 2013 or
• bearophile (9/12) Mar 16 2013 import std.array;
• John Colvin (33/39) Mar 16 2013 There are very many different ways of doing this, here are a few.
• John Colvin (4/46) Mar 16 2013 or, as bearophile points out, use std.array.replicate
• H. S. Teoh (21/27) Mar 16 2013 [...]

"Peter Sommerfeld" <noreply rubrica.at> writes:

Cannot find a reference: What is the best way
to catenate a string multiple times ?
Unfortunately this this does not work ;-)

string tab = "..";
tab = tab * 4; // -> "........"

Peter

1100110 <0b1100110 gmail.com> writes:

On 03/16/2013 10:29 AM, Peter Sommerfeld wrote:
 Cannot find a reference: What is the best way
 to catenate a string multiple times ?
 Unfortunately this this does not work ;-)

 string tab = "..";
 tab = tab * 4; // -> "........"

 Peter

foreach(0..4)
	write("...");

1100110 <0b1100110 gmail.com> writes:

On 03/16/2013 10:39 AM, 1100110 wrote:
 On 03/16/2013 10:29 AM, Peter Sommerfeld wrote:
 Cannot find a reference: What is the best way
 to catenate a string multiple times ?
 Unfortunately this this does not work ;-)

 string tab = "..";
 tab = tab * 4; // -> "........"

 Peter



foreach(0..4)
 write("...");

or
str = str ~ "...";

I shoulda proofread that.

"bearophile" <bearophileHUGS lycos.com> writes:

Peter Sommerfeld:

 Cannot find a reference: What is the best way
 to catenate a string multiple times ?


import std.array;

void main() {
     string tab = "..";
     tab = tab.replicate(4);
}


 Unfortunately this this does not work ;-)

D has vector ops, so I guess it's better to not add that.

Bye,
bearophile

"John Colvin" <john.loughran.colvin gmail.com> writes:

On Saturday, 16 March 2013 at 15:29:03 UTC, Peter Sommerfeld 
wrote:
 Cannot find a reference: What is the best way
 to catenate a string multiple times ?
 Unfortunately this this does not work ;-)

 string tab = "..";
 tab = tab * 4; // -> "........"

 Peter

There are very many different ways of doing this, here are a few.

using template recursion:

//Repeats string "s" size_t "num" times at compile-time
template RepeatString (string s, size_t num)
{
     static if(num == 0)
         const RepeatString = "";
     else
         const RepeatString = s ~ RepeatString!(s, num-1);
}


or for fast runtime performance (also works at compile-time), 
something like this:

//appends any array to itself multiple times.
T[] concat(T)(T[] arr, size_t num_times)
{
     auto app = appender!(T[])(arr);
     app.reserve(num_times);

     foreach(i; 0..num_times)
         app ~= arr;

     return app.data;
}


simpler but slower:

T[] concat_slow(T)(T[] arr, size_t num_times)
{
     auto result = arr;
     foreach(i; 0..num_times)
         result ~= arr;
     return result;
}


If you needed extreme performance there are faster ways, but they 
are much longer and more complex.

"John Colvin" <john.loughran.colvin gmail.com> writes:

On Saturday, 16 March 2013 at 15:58:32 UTC, John Colvin wrote:
 On Saturday, 16 March 2013 at 15:29:03 UTC, Peter Sommerfeld 
 wrote:
 Cannot find a reference: What is the best way
 to catenate a string multiple times ?
 Unfortunately this this does not work ;-)

 string tab = "..";
 tab = tab * 4; // -> "........"

 Peter

 There are very many different ways of doing this, here are a 
 few.

 using template recursion:

 //Repeats string "s" size_t "num" times at compile-time
 template RepeatString (string s, size_t num)
 {
     static if(num == 0)
         const RepeatString = "";
     else
         const RepeatString = s ~ RepeatString!(s, num-1);
 }


 or for fast runtime performance (also works at compile-time), 
 something like this:

 //appends any array to itself multiple times.
 T[] concat(T)(T[] arr, size_t num_times)
 {
     auto app = appender!(T[])(arr);
     app.reserve(num_times);

     foreach(i; 0..num_times)
         app ~= arr;

     return app.data;
 }


 simpler but slower:

 T[] concat_slow(T)(T[] arr, size_t num_times)
 {
     auto result = arr;
     foreach(i; 0..num_times)
         result ~= arr;
     return result;
 }


 If you needed extreme performance there are faster ways, but 
 they are much longer and more complex.

or, as bearophile points out, use std.array.replicate

I should really read over phobos again, I keep forgetting 
functions exist...

"H. S. Teoh" <hsteoh quickfur.ath.cx> writes:

On Sat, Mar 16, 2013 at 04:29:02PM +0100, Peter Sommerfeld wrote:
 Cannot find a reference: What is the best way
 to catenate a string multiple times ?
 Unfortunately this this does not work ;-)
 
 string tab = "..";
 tab = tab * 4; // -> "........"

[...]

You could define something like this:

	string x(string a, int n) {
		import std.array;
		auto app = appender!string(a);
		while (--n) {
			app.put(a);
		}
		return app.data;
	}

	void main() {
		// prints "abcabcabc"
		writeln("abc".x(3));
	}

It's not as nice as "abc"*3, but unfortunately opBinary only works when
declared inside the class/struct; UFCS doesn't pick it up, so it doesn't
work on native types.


T

-- 
Why do conspiracy theories always come from the same people??