为什么我会收到有关 Delphi 不兼容类型(数组和动态数组)的错误消息? [英] Why am I receiving an error about Delphi incompatible types (array and dynamic array)?

问题描述

(编辑:这是继在面向 Windows 的 Delphi 应用程序中计数的对象引用，以及如果是，它的目的是什么? 和 Delphi 中的动态数组和内存管理).

我有两个类(TGenericHoldingSummary、TGenericHoldingResultSet)和一个记录(TGenericHoldingResult).

I have two classes (TGenericHoldingSummary, TGenericHoldingResultSet) and one record (TGenericHoldingResult).

• TGenericHoldingSummary 包含一个 TGenericHoldingResultSet，它被设置为 nil 并在需要时从数据库中延迟加载.
• TGenericHoldingResultSet 包含一个动态的 TGenericHoldingResult 记录数组.

• TGenericHoldingSummary contains a single TGenericHoldingResultSet, which is set to nil and lazy-loaded from the database if and when required.
• The TGenericHoldingResultSet contains a dynamic array of TGenericHoldingResult records.

在下面，错误是在 TGenericHoldingResultSet 构造函数中的赋值.

In the below, the error is at the assignment in the TGenericHoldingResultSet constructor.

TGenericHoldingResult = record
  code : Integer;
  level : String;
  msg : String;
end;

TGenericHoldingResultSet = class(TObject)
  public
    // Lifecycle
    constructor Create(parent : TGenericHoldingSummary; resArr : Array of TGenericHoldingResult);
    destructor Destroy;
    // Accessors
    function ResultCount() : Integer;
    function Result(i : Integer) : TGenericHoldingResult;
  private
    // Variables
    summary : TGenericHoldingSummary;
    resultArray : Array of TGenericHoldingResult;
end;

TGenericHoldingSummary = class(TObject)
public
  // Note that the summary object 'owns' the results, and deallocates
  // its memory in the destructor.
  function getResultSet: TGenericHoldingResultSet;
private
  // Member variables
  resultSet: TGenericHoldingResultSet;
end;

// Note that the summary object 'owns' the results, and deallocates
// its memory in the destructor.
function TGenericHoldingSummary.getResultSet() : TGenericHoldingResultSet;
var
  sql : String;
  i : Integer;
  resultArray : Array of TGenericHoldingResult;
begin
  if resultSet = nil then
  begin
    // Get results via SQL.
    SetLength(resultArray, holding.clientDataSet.RecordCount);

    for i := 0 to holding.clientDataSet.RecordCount - 1 do
    begin
      resultArray[i].code := holding.clientDataSet.FieldByName('code').AsInteger;
      resultArray[i].level := holding.clientDataSet.FieldByName('level').AsString;
      resultArray[i].msg := holding.clientDataSet.FieldByName('message').AsString;
    end;

    resultSet := TGenericHoldingResultSet.Create(self, resultArray);
  end;

  result := resultSet;
end;

// Lifecycle
constructor TGenericHoldingResultSet.Create(parent : TGenericHoldingSummary; resArr : Array of TGenericHoldingResult);
begin
  summary := parent;
  // The following *should* work, shouldn't it?
  // E.g., seeing as dynamic arrays a reference counted in Delphi for
  // all platforms, this should simply increment the reference count.
  resultArray := resArr;
end;

错误如下:

[DCC Error] GenericHolding.pas(302): E2010 Incompatible types: 'Dynamic array' and 'Array'

推荐答案

不能将开放数组分配给动态数组.请参阅开放阵列参数.

You cannot assign an open array to a dynamic array. See Open Array Parameters.

注意:开放数组参数的语法类似于动态数组类型的语法，但它们的含义并不相同.前面的示例创建了一个函数，该函数采用任何 Char 元素数组，包括(但不限于)动态数组.要声明必须是动态数组的参数，您需要指定一个类型标识符:

Note: The syntax of open array parameters resembles that of dynamic array types, but they do not mean the same thing. The previous example creates a function that takes any array of Char elements, including (but not limited to) dynamic arrays. To declare parameters that must be dynamic arrays, you need to specify a type identifier:

type TDynamicCharArray = array of Char;
function Find(const A: TDynamicCharArray): Integer;

开放数组 用例的一个很好的总结以及与动态数组的区别可以在这里找到:打开数组参数.

A good summary of the use case of open arrays and the difference with a dynamic array can be found here: Open array parameters.

如果你有一个支持泛型的 Delphi 版本，可以声明构造函数头:

If you have a Delphi version that supports generics, it is possible to declare the constructor header:

constructor TGenericHoldingResultSet.Create(parent : TGenericHoldingSummary; 
  const resArr : TArray<TGenericHoldingResult>);

和你的 resultArray 作为 TArray.

这将避免必须为数组声明特定类型.

This will avoid having to declare a specific type for the array.

正如 David 所指出的，开放数组有一个好处，因为它们有更广泛的用例，应该尽可能使用.

As noted by David, open arrays have a benefit since they have a broader use case, and should be used when possible.

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