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digitalmars.D.learn - attribute length missing in std.array: Appender

reply "Andre" <andre s-e-a-p.de> writes:
Hi,

I implement a network protocol and use an Appender!(ubyte[])().
I have following issue. The first three bytes I have to fill,
the following bytes are reserved and must be 0. In this example
the overall header length must be 8.

import std.array: appender;
const HEADER_LENGTH = 8;
	
auto app = appender!(ubyte[])();
app.put(cast(ubyte)40);
app.put(cast(ubyte)5);
app.put(cast(ubyte)234);
// ... add 5 times 0
// variable length body will follow

In case of dynamic array I can simple set the length to 8.
Appender doesn't have a length attribute.

Is there some other nice D functionaliy I can use?
Maybe some functionality in std.array is missing: app.fill(0, 
HEADER_LENGTH)?
Currently I do a work around with a for loop.

Kind regards
André
Nov 27 2014
next sibling parent reply "Marc =?UTF-8?B?U2Now7x0eiI=?= <schuetzm gmx.net> writes:
On Thursday, 27 November 2014 at 16:08:13 UTC, Andre wrote:

 Hi,

 I implement a network protocol and use an Appender!(ubyte[])().
 I have following issue. The first three bytes I have to fill,
 the following bytes are reserved and must be 0. In this example
 the overall header length must be 8.

 import std.array: appender;
 const HEADER_LENGTH = 8;
 	
 auto app = appender!(ubyte[])();
 app.put(cast(ubyte)40);
 app.put(cast(ubyte)5);
 app.put(cast(ubyte)234);
 // ... add 5 times 0
 // variable length body will follow

 In case of dynamic array I can simple set the length to 8.
 Appender doesn't have a length attribute.

 Is there some other nice D functionaliy I can use?
 Maybe some functionality in std.array is missing: app.fill(0, 
 HEADER_LENGTH)?
 Currently I do a work around with a for loop.

 Kind regards
 André


You can initialize the appender with an existing array, or put an 
entire array into it at once:

     import std.array: appender;
     ubyte[] temp;
     temp.reserve(8);  // reserve first, so that only one 
allocation happens
     temp[0 .. 3] = [40, 5, 234];
     temp.length = 8;
     auto app = appender!(ubyte[])(temp);
     // or:
     app.put(temp);

The array will not be copied when the appender is constructed.
Nov 27 2014
parent "andre" <Andre s-e-a-p.de> writes:
Thanks a lot for the help.

Kind regards
André



On Thursday, 27 November 2014 at 17:29:50 UTC, Marc Schütz wrote:

 On Thursday, 27 November 2014 at 16:08:13 UTC, Andre wrote:

 Hi,

 I implement a network protocol and use an Appender!(ubyte[])().
 I have following issue. The first three bytes I have to fill,
 the following bytes are reserved and must be 0. In this example
 the overall header length must be 8.

 import std.array: appender;
 const HEADER_LENGTH = 8;
 	
 auto app = appender!(ubyte[])();
 app.put(cast(ubyte)40);
 app.put(cast(ubyte)5);
 app.put(cast(ubyte)234);
 // ... add 5 times 0
 // variable length body will follow

 In case of dynamic array I can simple set the length to 8.
 Appender doesn't have a length attribute.

 Is there some other nice D functionaliy I can use?
 Maybe some functionality in std.array is missing: app.fill(0, 
 HEADER_LENGTH)?
 Currently I do a work around with a for loop.

 Kind regards
 André


 You can initialize the appender with an existing array, or put 
 an entire array into it at once:

     import std.array: appender;
     ubyte[] temp;
     temp.reserve(8);  // reserve first, so that only one 
 allocation happens
     temp[0 .. 3] = [40, 5, 234];
     temp.length = 8;
     auto app = appender!(ubyte[])(temp);
     // or:
     app.put(temp);

 The array will not be copied when the appender is constructed.
Nov 27 2014
prev sibling parent reply =?UTF-8?B?QWxpIMOHZWhyZWxp?= <acehreli yahoo.com> writes:
On 11/27/2014 08:08 AM, Andre wrote:


 import std.array: appender;
 const HEADER_LENGTH = 8;

 auto app = appender!(ubyte[])();
 app.put(cast(ubyte)40);
 app.put(cast(ubyte)5);
 app.put(cast(ubyte)234);
 // ... add 5 times 0


A fancy way: :)

import std.range;

// ...

     app.put(repeat(cast(ubyte)0).take(5));

Ali
Nov 28 2014
parent reply "bearophile" <bearophileHUGS lycos.com> writes:
Ali Çehreli:


 auto app = appender!(ubyte[])();
 app.put(cast(ubyte)40);
 app.put(cast(ubyte)5);
 app.put(cast(ubyte)234);
 // ... add 5 times 0


 A fancy way: :)

 import std.range;

 // ...

     app.put(repeat(cast(ubyte)0).take(5));


Now we have a better syntax for implicit casts:

void main() {
     import std.array, std.range;
     Appender!(ubyte[]) app;
     app.put(ubyte(0).repeat.take(5));
}


Single line, but not lazy:

void main() {
     import std.array, std.range;
     Appender!(ubyte[]) app = ubyte(0).repeat.take(5).array;
}


But I have a question too. What's the best way to append several 
lazy items to a dynamic array? This doesn't work:

void main() {
     import std.array, std.range;
     int[] arr;
     arr.put(only(1, 2, 3));
}

Bye,
bearophile
Nov 28 2014
parent reply =?UTF-8?B?QWxpIMOHZWhyZWxp?= <acehreli yahoo.com> writes:
On 11/28/2014 12:44 AM, bearophile wrote:


 Now we have a better syntax for implicit casts:


[...]


      app.put(ubyte(0).repeat.take(5));


Much better! :)


 But I have a question too. What's the best way to append several lazy
 items to a dynamic array? This doesn't work:

 void main() {
      import std.array, std.range;
      int[] arr;
      arr.put(only(1, 2, 3));
 }


I don't think there is a better way in Phobos. (?) The following trivial 
function would do as long as the array has room at the end, which 
requires that it is "safe to append":

void expandWith(A, R)(ref A arr, R range)
{
     foreach (e; range) {
         arr ~= e;
     }
}

void main() {
     import std.range;

     int[] arr = [ 42 ];

     // Ensure that there is room for new elements
     arr.reserve(100);
     assumeSafeAppend(arr);

     const oldPlace = arr.ptr;
     arr.expandWith(only(1, 2, 3));
     const newPlace = arr.ptr;

     assert(newPlace == oldPlace);
}

Ali
Nov 28 2014
parent "bearophile" <bearophileHUGS lycos.com> writes:
Ali Çehreli:


 void expandWith(A, R)(ref A arr, R range)
 {
     foreach (e; range) {
         arr ~= e;
     }
 }


I'd like a function like that in Phobos (with a little 
improvement: when the length of the given range is available 
inside expandWith, it should first extend the capacity to 
increase performance a little). But I'd call it "extend" as in 
Python.

Bye,
bearophile
Nov 28 2014