www.digitalmars.com         C & C++   DMDScript  

digitalmars.D.learn - Appenders and Arrays

reply "default0" <Kevin.Labschek gmx.de> writes:
Hello

A simple thing I stumbled across:

int main()
{
     import std.stdio;
     import std.range;

     int[] d;
     d ~= 10;
     d ~= 20;
     d.put(5);
     writeln(d);

     return 0;
}

Appenders work fine as output ranges, but arrays do not. The 
above code prints "20" (ie the 10 is removed). Is "put" not 
supposed to mean "append one element"?

Further, while the following compiles fine but runs really odd, 
the following does not compile:

int main()
{
     import std.stdio;
     import std.range;

     char[] c;
     c ~= 'a';
     c ~= 'b';
     c.put('c');
     writeln(c);

     return 0;
}

C:\dmd\src\phobos\std\range.d(9,9): Error: static assert  "Cannot 
put a char into a char[]." (Test)

I am puzzled by
1) Why I cannot put a char into a char[] (even though I can 
totally append them)
2) Why put removes elements from arrays

Hopefully somebody can help me clear my confusion about this (yes 
in the meantime I can just use Appenders, but you know, still 
wondering).
Sep 01 2015
parent reply Steven Schveighoffer <schveiguy yahoo.com> writes:
On 9/1/15 12:49 PM, default0 wrote:

 Hello

 A simple thing I stumbled across:

 int main()
 {
      import std.stdio;
      import std.range;

      int[] d;
      d ~= 10;
      d ~= 20;
      d.put(5);
      writeln(d);

      return 0;
 }

 Appenders work fine as output ranges, but arrays do not. The above code
 prints "20" (ie the 10 is removed). Is "put" not supposed to mean
 "append one element"?


put into an slice does not append, it fills in the front. This is 
because the "target" of a slice is the data it points at.

Think of it as a buffer that you want to fill:

int[20] buf;
int[] outputRange = buf[];
outputRange.put(10);
outputRange.put(20);

assert(buf[0..2] == [10,20]);


 Further, while the following compiles fine but runs really odd, the
 following does not compile:

 int main()
 {
      import std.stdio;
      import std.range;

      char[] c;
      c ~= 'a';
      c ~= 'b';
      c.put('c');
      writeln(c);

      return 0;
 }

 C:\dmd\src\phobos\std\range.d(9,9): Error: static assert  "Cannot put a
 char into a char[]." (Test)

 I am puzzled by
 1) Why I cannot put a char into a char[] (even though I can totally
 append them)


That seems like a bug. put has specific code to deal with putting 
characters into character ranges. Please file 
https://issues.dlang.org/enter_bug.cgi

-Steve
Sep 01 2015
next sibling parent "default0" <Kevin.Labschek gmx.de> writes:
On Tuesday, 1 September 2015 at 17:20:49 UTC, Steven 
Schveighoffer wrote:

 On 9/1/15 12:49 PM, default0 wrote:

 Hello

 A simple thing I stumbled across:

 int main()
 {
      import std.stdio;
      import std.range;

      int[] d;
      d ~= 10;
      d ~= 20;
      d.put(5);
      writeln(d);

      return 0;
 }

 Appenders work fine as output ranges, but arrays do not. The 
 above code
 prints "20" (ie the 10 is removed). Is "put" not supposed to 
 mean
 "append one element"?


 put into an slice does not append, it fills in the front. This 
 is because the "target" of a slice is the data it points at.

 Think of it as a buffer that you want to fill:

 int[20] buf;
 int[] outputRange = buf[];
 outputRange.put(10);
 outputRange.put(20);

 assert(buf[0..2] == [10,20]);


 Further, while the following compiles fine but runs really 
 odd, the
 following does not compile:

 int main()
 {
      import std.stdio;
      import std.range;

      char[] c;
      c ~= 'a';
      c ~= 'b';
      c.put('c');
      writeln(c);

      return 0;
 }

 C:\dmd\src\phobos\std\range.d(9,9): Error: static assert  
 "Cannot put a
 char into a char[]." (Test)

 I am puzzled by
 1) Why I cannot put a char into a char[] (even though I can 
 totally
 append them)


 That seems like a bug. put has specific code to deal with 
 putting characters into character ranges. Please file 
 https://issues.dlang.org/enter_bug.cgi

 -Steve



Thanks a lot for the clear explanation!
Issue has been created here: 
https://issues.dlang.org/show_bug.cgi?id=14998
Sep 01 2015
prev sibling parent reply Daniel Kozak via Digitalmars-d-learn <digitalmars-d-learn puremagic.com> writes:
Dne 1.9.2015 v 19:20 Steven Schveighoffer via Digitalmars-d-learn napsal(a):

 On 9/1/15 12:49 PM, default0 wrote:

 Hello

 A simple thing I stumbled across:

 int main()
 {
      import std.stdio;
      import std.range;

      int[] d;
      d ~= 10;
      d ~= 20;
      d.put(5);
      writeln(d);

      return 0;
 }

 Appenders work fine as output ranges, but arrays do not. The above code
 prints "20" (ie the 10 is removed). Is "put" not supposed to mean
 "append one element"?


 put into an slice does not append, it fills in the front. This is 
 because the "target" of a slice is the data it points at.

 Think of it as a buffer that you want to fill:

 int[20] buf;
 int[] outputRange = buf[];
 outputRange.put(10);
 outputRange.put(20);

 assert(buf[0..2] == [10,20]);


So it is something like this?:

int main()
{
     import std.stdio;
     import std.range;

     int[] d;
     d ~= [10];
     d ~= [20];
     d.front = 5;
     d.popFront();
     writeln(d);

     return 0;
}
Sep 01 2015
parent reply Steven Schveighoffer <schveiguy yahoo.com> writes:
On 9/1/15 3:13 PM, Daniel Kozak via Digitalmars-d-learn wrote:

 Dne 1.9.2015 v 19:20 Steven Schveighoffer via Digitalmars-d-learn
 napsal(a):

 On 9/1/15 12:49 PM, default0 wrote:

 Hello

 A simple thing I stumbled across:

 int main()
 {
      import std.stdio;
      import std.range;

      int[] d;
      d ~= 10;
      d ~= 20;
      d.put(5);
      writeln(d);

      return 0;
 }

 Appenders work fine as output ranges, but arrays do not. The above code
 prints "20" (ie the 10 is removed). Is "put" not supposed to mean
 "append one element"?


 put into an slice does not append, it fills in the front. This is
 because the "target" of a slice is the data it points at.

 Think of it as a buffer that you want to fill:

 int[20] buf;
 int[] outputRange = buf[];
 outputRange.put(10);
 outputRange.put(20);

 assert(buf[0..2] == [10,20]);


 So it is something like this?:

 int main()
 {
      import std.stdio;
      import std.range;

      int[] d;
      d ~= [10];
      d ~= [20];
      d.front = 5;
      d.popFront();
      writeln(d);

      return 0;
 }


I'm not following your code. What is the question?

-Steve
Sep 01 2015
parent =?UTF-8?B?QWxpIMOHZWhyZWxp?= <acehreli yahoo.com> writes:
On 09/01/2015 02:16 PM, Steven Schveighoffer wrote:> On 9/1/15 3:13 PM, 
Daniel Kozak via Digitalmars-d-learn wrote:

 Dne 1.9.2015 v 19:20 Steven Schveighoffer via Digitalmars-d-learn
 napsal(a):

 On 9/1/15 12:49 PM, default0 wrote:

 Hello

 A simple thing I stumbled across:

 int main()
 {
      import std.stdio;
      import std.range;

      int[] d;
      d ~= 10;
      d ~= 20;
      d.put(5);
      writeln(d);

      return 0;
 }

 Appenders work fine as output ranges, but arrays do not. The above 








code

 prints "20" (ie the 10 is removed). Is "put" not supposed to mean
 "append one element"?


 put into an slice does not append, it fills in the front. This is
 because the "target" of a slice is the data it points at.

 Think of it as a buffer that you want to fill:

 int[20] buf;
 int[] outputRange = buf[];
 outputRange.put(10);
 outputRange.put(20);

 assert(buf[0..2] == [10,20]);


 So it is something like this?:

 int main()
 {
      import std.stdio;
      import std.range;

      int[] d;
      d ~= [10];
      d ~= [20];
      d.front = 5;
      d.popFront();
      writeln(d);

      return 0;
 }


 I'm not following your code. What is the question?

 -Steve


I think Daniel is asking whether .put() on a slice is the equivalent of 
assigning to front() and then popFront(). The answer is yes.



http://ddili.org/ders/d.en/ranges.html#ix_ranges.slice,%20as%20OutputRange

Ali
Sep 01 2015