我可以在Delphi / Pascal中一次性分配数组中的项目吗？

Question

I want to do something like in PHP, Python and most other programming languages:

my_array_name = [128, 38459, 438, 23674...] 

So I tried to replicate this in Delphi/Pascal the best I could:

HSVtoRGB := [0, 0, 0];

(this is for a function which returns an RGB array given HSV values.)

But I am getting errors:

[DCC Error] Unit2.pas(44): E2001 Ordinal type required
[DCC Error] Unit2.pas(45): E2010 Incompatible types: 'HSVRealArray' and 'Set'

Any idea? This is school work - but my teacher didn't know the answer.

Answer 1

When it comes to dynamic arrays, yes:

type
  TIntArray = array of integer;

procedure TForm1.Button1Click(Sender: TObject);
var
  MyArr: TIntArray;
begin
  MyArr := TIntArray.Create(10, 20, 30, 40);
end;

When it comes to static arrays, you need to write a helper function:

type
  TIntArray = array[0..2] of integer;

function IntArray(const A, B, C: integer): TIntArray;
begin
  result[0] := A;
  result[1] := B;
  result[2] := C;
end;

procedure TForm1.Button1Click(Sender: TObject);
var
  MyArr: TIntArray;
begin
  MyArr := IntArray(10, 20, 30);
end;

This resembles how the Point function creates a TPoint record. (Records and arrays are not the same thing, though.)

Answer 2

This is an area where Delphi turns something that is a simple one-line assignment statement in most languages into something more complicated.

One approach would to declare the value as a typed constant:

type
  HSVRealArray = array[1..3] of real;
const
  constHSVVal: HSVRealArray = (0, 0, 0);
var
  currentValue: HSVRealArray;
begin
  currentValue := constHSVVal;
end;

Another approach is to create utility functions that return the type you need:

function MakeHSVRealArray(H, S, V: Real): HSVRealArray;
begin
  Result[1] := H;
  Result[2] := S;
  Result[3] := V;
end;

currentValue := MakeHSVRealArray(0,0,0);

Answer 3

With some extra work, you can achieve a clean implementation:

var
    x: TRGB;
begin
    x := TRGB.Init(0,0,0);
end;

---

TRGB = record
    Red, Green, Blue: real;
    class function Init(r,g,b: real): TRGB; static;
end;

class function TRGB.Init(r, g, b: real): TRGB;
begin
    Result.Red := r;
    Result.Green := g;
    Result.Blue := b;
end;

Answer 4

For array handling, array initialization and array constant declarations, Delphi doesn't make simple things simple.

In some situations similar to yours, I initialize the array with a utility function taking one open array parameter and returning the appropiate static string.

const
    MaxArray = 10;
type
    TRealStaticArray = array[0..MaxArray] of Real;

function RealArray(const AnArray: array of real):TRealStaticArray;
    const DefaultValue=0.0;
    var i: integer;
    begin
        // EDIT: commented out, thanks Serg. for i:= 0 to low(AnArray)-1 do result[i]:=DefaultValue;
        for i:= High(AnArray)+1 to MaxArray do
            result[i]:=DefaultValue;
        for i:= Low(AnArray) to High(AnArray) do
            if (i>=0) and (i<=MaxArray) then
                result[i]:=AnArray[i];
    end;

Use it this way:

 var MyArray: TRealStaticArray;
 ...
 MyArray := RealArray([10.0, 20.0, 30.0]);

Answer 5

Delphi-XE7 introduced a new syntax for dynamic array initialization.

// compile time const declaration of dynamic array
const
  my_ConstArray_name: TArray<Integer> = [128, 38459, 438, 23674];

// compile time var declaration of dynamic array
var
  my_VarArray_name: TArray<Integer> = [128, 38459, 438, 23674];

Runtime assignment of dynamic arrays:

var
  a : TArray<Integer>;
begin
  a := [1,2,3];

Unfortunately this syntax cannot be used on ordinary static arrays:

Type
  TMyArray = array[0..3] of Integer;  

const
  cMyArray: TMyArray = [0,1,2,3]; // E2010 Incompatible types: 'TMyArray' and 'Set'
  cMyArray: TMyArray = (0,1,2,3); // Works, as in all Delphi versions

var
  MyArray: TMyArray;
begin
  // This fails as well
  MyArray := [0,1,2,3]; // E2010 Incompatible types: 'TMyArray' and 'Set'
  MyArray := (0,1,2,3); // E2029 ')' expected but ',' found  
  //-----------^-------

  // This works in all Delphi versions !
  MyArray := cMyArray;

Answer 6

I know this is an old post, but I came across this while looking into the auto-assignment technique for Delphi. This post has a very nice explanation, along with a way to auto-assign an array of records:

http://delphi.about.com/od/adptips2006/qt/const_array.htm

Unfortunately, the initialization can only be done with native or record types. Class objects need a helper function as others have shown above.

Answer 7

Can you try something like that:

TRGB = record
      Red  : integer;
      Green: integer;
      Bklue: integer;
  end;

var Variable:TRGB;

Variable.Red:=0;
Variable.Green:=0;
Variable.Blue:=0;

Answer 8

Putting aside the general question, I'd like to point out that the specific use-case was never going to work anyway: Delphi can't return on the stack the contents of an array of unknown length.

The return type of a function needs to be known by the calling code. It may be a pointer to the heap: it may even be a memory-managed object on the stack: but it is not permitted to be an undefined number of bytes on the stack, decided dynamically by the target function.

And in many other languages, the example

return (0,0,0)  //return pointer to automatic allocation

would be undefined, even if the compiler lets you do it.

A common method of defining, using and returning const values is

int myarray[8] = {128, 38459, 438 ... 23674};
memcpy (myparam, myArray, sizeof (myArray)); 

... and you can do that in Delphi

Answer 9

[0, 0, 0] is a set in Delphi. (0, 0, 0) is an array constant in Delphi! Just use:

HSVtoRGB := (0, 0, 0);

(Unless HSVtoRGB is a dynamic array. Did you declare it as var HSVtoRGB: array[1..3] of integer; or something similar?