Spring4D TDistinctIterator<string>.ToArray() not working?

user_479179 0
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I want to use the Spring4D TDistinctIterator to get the distinct Values in a TDictionary. Therefore I have the following code:

var
  d: TDictionary<Integer, String>;
  v: Vector<String>;
begin
  d := TDictionary<Integer, String>.Create();
  d.Add(1, 'test');
  d.Add(2, 'test');
  d.Add(3, 'test');

  v := TDistinctIterator<string>.Create(d.Values, nil).ToArray();
end;

However, this gives an access violation in the ToArray. Is this a bug or should I use the iterator in another way to achieve the same result?

spring4d delphi
1 Answers

Your problem is that you are using the implementing classes rather then an interface based approach. It's important to realise that much of the spring4d code is intended to be used via interfaces and you typically should not refer to the implementing classes behind those interfaces.

What is happening in your case is that TDistinctIterator<T> has lifetime managed by reference counting. Your code does not handle that lifetime management correctly, and the TDistinctIterator<String> instance is destroyed before you call ToArray, leading to the access violation.

As well as the problem with TDistinctIterator<T>, your code also doesn't handle the lifetime of the dictionary correctly.

Your code should look like this:

var
  d: IDictionary<Integer, String>;
  v: Vector<String>;
begin
  d := TCollections.CreateDictionary<Integer, String>();
  d.Add(1, 'test');
  d.Add(2, 'test');
  d.Add(3, 'test');

  v := TEnumerable.Distinct<String>(d.Values).ToArray();
end;

Note also that when written this way you can remove Spring.Collections.Dictionaries and Spring.Collections.Extensions from your uses list. The only two units you need are Spring and Spring.Collections.

user_5050880
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