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Variant open array parameters

Variant open array parameters allow you to pass an array of differently-typed expressions to a single procedure or function. To define a routine with a variant open array parameter, specify array of const as the parameter’s type. Thus

procedure DoSomething(A: array of const);

declares a procedure called DoSomething that can operate on heterogeneous arrays.

The array of const construction is equivalent to array of TVarRec. TVarRec, declared in the System unit, represents a record with a variant part that can hold values of integer, Boolean, character, real, string, pointer, class, class reference, interface, and variant types. TVarRec’s VType field indicates the type of each element in the array. Some types are passed as pointers rather than values; in particular, long strings are passed as Pointer and must be typecast to string.

The following example uses a variant open array parameter in a function that creates a string representation of each element passed to it and concatenates the results into a single string. The string-handling routines called in this function are defined in SysUtils.

function MakeStr(const Args: array of const): string;

const

BoolChars: array[Boolean] of Char = ('F', 'T');

var

I: Integer;

begin

Result := '';

for I := 0 to High(Args) do

with Args[I] do

case VType of

vtInteger: Result := Result + IntToStr(VInteger);

vtBoolean: Result := Result + BoolChars[VBoolean];

vtChar: Result := Result + VChar;

vtExtended: Result := Result + FloatToStr(VExtended^);

vtString: Result := Result + VString^;

vtPChar: Result := Result + VPChar;

vtObject: Result := Result + VObject.ClassName;

vtClass: Result := Result + VClass.ClassName;

vtAnsiString: Result := Result + string(VAnsiString);

vtCurrency: Result := Result + CurrToStr(VCurrency^);

vtVariant: Result := Result + string(VVariant^);

vtInt64: Result := Result + IntToStr(VInt64^);

end;

We can call this function using an open array constructor (see Open array constructors). For example,

MakeStr(['test', 100, ' ', True, 3.14159, TForm])

returns the string “test100 T3.14159TForm".

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变体开放数组参数

变体开发数组参数允许向单个过程或函数传递不同类型表达式的数组。要定义含有变体开放数组参数的例程，需要指定array of const作为参数类型。如，