Function prototype: Difference between revisions
Added Delphi example
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void main() {}</lang>
=={{header|Delphi}}==
{{libheader| System.SysUtils}}
In Delphi, prototype function is named Class/Record Helper. For now, is not possible has more then one helper active in a same object, if two or more was declareted, just the present in the last Unit declareted will be active, the others will be ignored. In case two or more helpers was declareted in same Unit, just the last helper declareted will be active. Can not inherit record helpers, but class helper can be.<br>
Patten: " identifierName = record helper for TypeIdentifierName"<br>
See [http://docwiki.embarcadero.com/RADStudio/Sydney/en/Class_and_Record_Helpers_(Delphi) Documentation] for more details.<br>
<lang Delphi>
program Function_prototype;
{$APPTYPE CONSOLE}
uses
System.SysUtils;
type
TIntArray = TArray<Integer>;
TIntArrayHelper = record helper for TIntArray
const
DEFAULT_VALUE = -1;
// A prototype declaration for a function that does not require arguments
function ToString(): string;
// A prototype declaration for a function that requires two arguments
procedure Insert(Index: Integer; value: Integer);
// A prototype declaration for a function that utilizes varargs
// varargs is not available, but a equivalent is array of const
procedure From(Args: array of const);
//A prototype declaration for a function that utilizes optional arguments
procedure Delete(Index: Integer; Count: Integer = 1);
//A prototype declaration for a function that utilizes named parameters
// Named parameters is not supported in Delphi
//Example of prototype declarations for subroutines or procedures
//(if these differ from functions)
procedure Sqr; //Procedure return nothing
function Averange: double; //Function return a value
end;
{ TIntHelper }
function TIntArrayHelper.Averange: double;
begin
Result := 0;
for var e in self do
Result := Result + e;
Result := Result / Length(self);
end;
procedure TIntArrayHelper.Delete(Index, Count: Integer);
begin
System.Delete(self, Index, Count);
end;
procedure TIntArrayHelper.From(Args: array of const);
var
I, Count: Integer;
begin
Count := Length(Args);
SetLength(self, Count);
if Count = 0 then
exit;
for I := 0 to High(Args) do
with Args[I] do
case VType of
vtInteger:
self[I] := VInteger;
vtBoolean:
self[I] := ord(VBoolean);
vtChar, vtWideChar:
self[I] := StrToIntDef(string(VChar), DEFAULT_VALUE);
vtExtended:
self[I] := Round(VExtended^);
vtString:
self[I] := StrToIntDef(VString^, DEFAULT_VALUE);
vtPChar:
self[I] := StrToIntDef(VPChar, DEFAULT_VALUE);
vtObject:
self[I] := cardinal(VObject);
vtClass:
self[I] := cardinal(VClass);
vtAnsiString:
self[I] := StrToIntDef(string(VAnsiString), DEFAULT_VALUE);
vtCurrency:
self[I] := Round(VCurrency^);
vtVariant:
self[I] := Integer(VVariant^);
vtInt64:
self[I] := Integer(VInt64^);
vtUnicodeString:
self[I] := StrToIntDef(string(VUnicodeString), DEFAULT_VALUE);
end;
end;
procedure TIntArrayHelper.Insert(Index, value: Integer);
begin
system.Insert([value], self, Index);
end;
procedure TIntArrayHelper.Sqr;
begin
for var I := 0 to High(self) do
Self[I] := Self[I] * Self[I];
end;
function TIntArrayHelper.ToString: string;
begin
Result := '[';
for var e in self do
Result := Result + e.ToString + ', ';
Result := Result + ']';
end;
begin
var val: TArray<Integer>;
val.From([1, '2', PI]);
val.Insert(0, -1); // insert -1 at position 0
writeln(' Array: ', val.ToString, ' ');
writeln(' Averange: ', val.Averange: 3: 2);
val.Sqr;
writeln(' Sqr: ', val.ToString);
Readln;
end.</lang>
{{out}}
<pre> Array: [-1, 1, 2, 3, ]
Averange: 1.25
Sqr: [1, 1, 4, 9, ]</pre>
Class helper example, with inherited helpers:<br>
Patten: " identifierName = class helper (ancestor list*) for TypeIdentifierName"<br>
Ancertor list is optional, and only will be used if this helper will inhret a parent helper.
{{libheader| System.SysUtils}}
{{libheader| System.Classes}}
<lang Delphi>
program Function_prototype_class;
{$APPTYPE CONSOLE}
uses
System.SysUtils,
System.Classes;
type
TStringListHelper1 = class helper for TStringList
constructor Create(FileName: TFileName); overload;
end;
TStringListHelper2 = class helper (TStringListHelper1) for TStringList
procedure SaveAndFree(FileName: TFileName);
end;
TStringListHelper3 = class helper (TStringListHelper2) for TStringList
procedure AddDateTime;
end;
{ TStringListHelper1 }
constructor TStringListHelper1.Create(FileName: TFileName);
begin
inherited Create;
if FileExists(FileName) then
LoadFromFile(FileName);
end;
{ TStringListHelper2 }
procedure TStringListHelper2.SaveAndFree(FileName: TFileName);
begin
SaveToFile(FileName);
Free;
end;
{ TStringListHelper3 }
procedure TStringListHelper3.AddDateTime;
begin
self.Add(DateToStr(now));
end;
begin
with TStringList.Create('d:\Text.txt') do
begin
AddDateTime;
SaveAndFree('d:\Text_done.txt');
end;
readln;
end.</lang>
=={{header|F Sharp|F#}}==
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