Using dynamic array constructors
lazarus / 62-General

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howardpc · 2016-07-03 14:29

The introduction of a Delphi-compatible class-like constructor syntax
in FPC 3.0.0
   http://wiki.freepascal.org/FPC_New_Features_3.0#Dynamic_array_const
ructors
is very welcome.

Is it possible to pass values to such a constructor dynamically (i.e.
not by typing literal values and commas into a source code editor)?

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Leledumbo · 2016-07-03 15:17

Do you have any example wish of how it should be done? i.e.: an
uncertain-to-work code you would like to type. Probably you just need
System.Copy.

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Thaddy · 2016-07-03 15:29

Urhm. Asking about scripting language features?

But anyway. Do you have an example in a comparable language like C or
C++?
Or some pseudo code of what you envisage?

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howardpc · 2016-07-03 18:24

I was looking for something that would interpret a comma-separated
list as a list of successive values in the array to be initialized.
Perhaps the following short example explains what I am after:

Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i program
Project1; {$H+} type  TStringDynArray = array of ansistring; const 
NumberStr = 'zero,one,two,three,four,five,six,seven'; var  nums:
TStringDynArray;  idx: integer = 0;  s: ansistring;begin  //
initialize array  nums:=TStringDynArray.create(NumberStr);  // display
array value(s)  for s in nums do begin    WriteLn('Index:',idx,'
',s);    Inc(idx);  end;end.
Compare this with the constructor
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i nums:=TStri
ngDynArray.create('zero','one','two','three','four','five','six','seve
n');

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Bart · 2016-07-03 18:38

How can the compiler ever know what you mean then?
Should it treat numberstring as one string (why should not the array
of strig contain a stringwith a comma), or as a commaseparated list?

Bart

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molly · 2016-07-03 19:48

You are absolutely right there Bart but, in the quest to instruct the
compiler to be able to do the right thing there:
Code: [Select]const
  NumberStrings = 'one', 'two';

Which produces a:
QuoteFatal: Syntax error, ";" expected but "," found

or perhaps more accurate:
Code: [Select]const
  NumberStrings = ('one', 'two');

Which produces a:
QuoteFatal: Syntax error, ")" expected but "," found


The way it's currently suppose to be:
Code: [Select]Const
  NumConst : Array[0..1] of ansistring = ('zero','one');
or:
Code: [Select]Var
  NumVar   : array[0..1] of ansistring = ('zero','one');

Maybe that is what howardpc (in basics) is/was referring to ?

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molly · 2016-07-03 20:52

Nevermind. Something like this seems to do what was asked for:
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i program
arrayhelper; {$MODE OBJFPC}{$MODESWITCH TYPEHELPERS} Uses 
StrUtils; type  TStringDynArray = array of ansistring; type 
TStringDynArrayHelper = type helper for TStringDynArray    class
function CreateFromDelimitedString(DelimString: String):
TStringDynArray static;  end; class function
TStringDynArrayHelper.CreateFromDelimitedString(DelimString: String):
TStringDynArray;var  num, i : Integer;begin  num :=
WordCount(DelimString, [',']);  SetLength(Result, num);  for i := 1 to
num do  begin    Result[i-1] := ExtractWord(i, DelimString, [',']); 
end;end; const  NumberStr =
'zero,one,two,three,four,five,six,seven';var  nums  :
TStringDynArray;  idx   : integer = 0;  s     : ansistring;begin  //
initialize array//  nums:=TStringDynArray.create(NumberStr); 
nums:=TStringDynArray.CreateFromDelimitedString(NumberStr);   //
display array value(s)  for s in nums do begin   
WriteLn('Index:',idx,' ',s);    Inc(idx);  end;end.

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ArtLogi · 2016-07-03 21:14

Molly how you can do the word extracting without passing the character
beforehand in the variable of the type of TSysCharSet? Is the key
those square brackets? I did fight "days" before getting it right in
FPC2.6.xx

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molly · 2016-07-03 21:33

Quote from: ArtLogi on July 03, 2016, 11:14:28 pmMolly how you can do
the word extracting without passing the character beforehand in the
variable of the type of TSysCharSet? Is the key those square brackets?
I did fight "days" before getting it right in FPC2.6.xx
Well, it is working for me since i can remember (but, i have bad
memory  ).

Maybe this will be able to help you ?
Code: [Select]program passer;

{$MODE OBJFPC}{$H+}
Uses
  SysUtils, StrUtils;

Const
  LowChars  = ['a'..'z'];

var
  HighChars : TSysCharset = ['A'..'Z'];

  num       : integer;
  S         : String;

begin
  S := 'I stand amid the roar of a surf-tormented shore, and 1 hold
within my hand Grains of the golden sand';
  num := wordcount(S, []);
  Writeln('num 0 = ', num);

  num := wordcount(S, LowChars);
  Writeln('num 1 = ', num);

  num := wordcount(S, HighChars);
  Writeln('num 2 = ', num);

  HighChars := ['a','b',','];
  num := wordcount(S, HighChars);
  Writeln('num 3 = ', num);

  include(highChars, ' ');
  num := wordcount(S, HighChars);
  Writeln('num 4 = ', num);
 
  HighChars := HighChars + ['1','2'];
  num := wordcount(S, HighChars);
  Writeln('num 5 = ', num);
end.

Also have a look at set operators.

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howardpc · 2016-07-03 21:39

Many thanks, molly.
I prefer a helper with no dependency on StrUtils.

Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i
TStringDynArrayHelper = type helper for TStringDynArray    class
function CreateCommaDelimited(const aCommaString: string):
TStringDynArray; static;  end; class function
TStringDynArrayHelper.CreateCommaDelimited(const aCommaString:
string): TStringDynArray;var  p: integer = 1;  len: integer = 0; 
predLen: integer;  s: string;begin  if (aCommaString = '') then   
Exit(nil);  repeat    s:='';    while (p <= Length(aCommaString)) and
(aCommaString[p] <> ',') do begin      s:=s + aCommaString[p];     
Inc(p);    end;    predLen:=len;    Inc(len);    SetLength(Result,
len);    Result[predLen]:=s;    Inc(p);  until (p >
Length(aCommaString));end;

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molly · 2016-07-03 23:19

Quote from: howardpc on July 03, 2016, 11:39:22 pmI prefer a helper
with no dependency on StrUtils.
Ah, indeed. i was being lazy  

As a matter of fact so lazy that i don't even wanted to use a type
helper 
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i program
arraymore; {$MODE OBJFPC} {.$DEFINE USETYPEHELPERS}{$IFDEF
USETYPEHELPERS}  {$MODESWITCH TYPEHELPERS}{$ENDIF} Uses  Heaptrc,
StrUtils; type  TStringDynArray = array of ansistring; {$IFDEF
USETYPEHELPERS} type  TStringDynArrayHelper = type helper for
TStringDynArray    class function
CreateFromDelimitedString(DelimString: String): TStringDynArray
static;  end; class function
TStringDynArrayHelper.CreateFromDelimitedString(DelimString: String):
TStringDynArray;var  num, i : Integer;begin  num :=
WordCount(DelimString, [',']);  SetLength(Result, num);  for i := 1 to
num do  begin    Result[i-1] := ExtractWord(i, DelimString, [',']); 
end;end; operator := (S : string): TStringDynArray;begin  Result :=
TStringDynArray.CreateFromDelimitedString(S);end; {$ELSE} operator :=
(S : string): TStringDynArray;var  num, i : Integer;begin  num :=
WordCount(S, [',']);  SetLength(Result, num);  for i := 1 to num do 
begin    Result[i-1] := ExtractWord(i, S, [',']); 
end;end; {$ENDIF}  const  NumberStr =
'zero,one,two,three,four,five,six,seven';var  nums  :
TStringDynArray;  idx   : integer = 0;  s     : ansistring;begin  //
initialize array//  nums:=TStringDynArray.create(NumberStr);//
 nums:=TStringDynArray.CreateFromDelimitedString(NumberStr);   nums :=
NumberStr;   // display array value(s)  for s in nums do begin   
WriteLn('Index:',idx,' ',s);    Inc(idx);  end;end. 
Mind-boggling in case you use these kind of things to much/deep.

Edit:
Hmz, seems i misunderstood something ?:
Code: [Select]const
  NumberStr = 'zero,one,two,three,four,five,six,seven';
var
  nums  : TStringDynArray = NumberStr;
produces:
Quote  Fatal: Syntax error, "NIL" expected but "identifier NUMBERSTR"
found
Is that not considered an assignment ? In which case it should be
covered by the explicit assignment operator ? If not the case, is
there a separate operator for such assignments ? (i was unable to find
in the docs)

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howardpc · 2016-07-04 06:44

Well
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i nums:
TStringDynArray = NumberString;is of course an assignment combined
with a declaration.

However it does not use the ':=' operator you have defined, so the
compiler rightly complains that the two types are incompatible.

BTW, do you know if recent Delphis now allow that C-style
initialization syntax in the declaration of variables?

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molly · 2016-07-04 07:07

Quote from: howardpc on July 04, 2016, 08:44:55 amBTW, do you know if
recent Delphis now allow that C-style initialization syntax in the
declaration of variables?
I have honestly no idea (we haven't used Delphi in ages).

But, i fully understand the desire to have such support. In fact i
would already settle for getting rid of the requirement to declare the
size of the array for a variable/constant. e.g. var x: TStringDynArray
= ('One','Two');.

TBH, for me the desire comes from porting c-code. so for me .. uh ..
it's about laziness

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ArtLogi · 2016-07-28 17:25

It's allways the laziness

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Thaddy · 2016-07-28 17:47

Quote from: howardpc on July 04, 2016, 08:44:55 amBTW, do you know if
recent Delphis now allow that C-style initialization syntax in the
declaration of variables?

If you mean:
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i program
a;{$IFDEF FPC}{$MODE DELPHI}{$ENDIF}{$APPTYPE CONSOLE}var a:integer =
1;begin  ..do something with aend. The answer is yes...

If you mean:Code: Pascal  [Select][+][-]window.onload = function(){var
x1 = document.getElementById("main_content_section"); if (x1) { var x
= document.getElementsByClassName("geshi");for (var i = 0; i program
b;{$IFDEF FPC}{$MODE DELPHI}{$ENDIF}{$APPTYPE CONSOLE}begin with var a
=1 do //declarations on the fly   begin   inc(a); end; end. The answer
is no, and I hope that never happens... as a language construct: You
will loose structure and oversight and your code becomes hard to read
for mere mortals.
Note the Delphi IDE has some support for things like that, but that is
not a language feature, but a refactoring/codecompletion feature of
the IDE.