Why am I receiving an error about Delphi incompatible types (array and dynamic array)?

Question

(EDIT: This is following on from Are objects reference counted in Windows-targeted Delphi applications, and if so, what is its purpose? and Dynamic arrays a

Answer 1

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

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;

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

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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>);

and your resultArray as TArray<TGenericHoldingResult>.

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

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