initializing objects in delphi

Question

as you know initializing object in c# is really handy and fast

    StudentName student2 = new StudentName
    {
        FirstName = "Craig",
        LastName = "Playstead",
    };

and

List<MyObject>.Add(new MyObject{a=1,b=2})

is it possible to initializing objects in Delphi like this?

There's no answer to your question other than "no". – David Heffernan Jul 21 '13 at 17:28 — David Heffernan, Jul 21 '13 at 17:28

score 5 · Accepted Answer · edited May 23 '17 at 12:13

As pointed out by others there is no object initializer syntax like there is in C#.

There are a few alternatives that come close.

ja-mesa already pointed out the with construct, though it's best to avoid this construct. You can see my blog for a (mostly) unbiased review of the pros and cons of using with as well as similar constructs in other languages and some alternatives.

Anonymous methods can be used for this though they're a little verbose and kind of ugly:

TMyObject.Create(procedure(var  FirstName, LastName: string)
                 begin
                   FirstName := 'Craig';
                   LastName := 'Playstead';
                 end);

A fluent interface can come fairly close to approximating this:
```
TMyObject.Create
         .FirstName('Craig')
         .LastName('Playstead');
```
The downside being that writing a fluent interface is time consuming and only pays off if you plan on using this class a lot or are writing a public api.

Constant records also come very close.

const
  MyRecord: TMyRecord =
  (
    FirstName : 'Craig';
    LastName : 'Playstead';
  );

The obvious drawback being that it is a constant

Another solution would be an overloaded constructor:
```
TMyObject.Create('Craig', 'Playstead');
```

Of course you could accomplish much the same thing by simply creating a temporary variable with a single character name.

var
  o: TMyObject;

begin
  o := TMyObject.Create;
  o.FirstName := 'Craig';
  o.LastName := 'Playstead';
  Result := o;
end;

score 4 · Answer 2 · answered Jul 21 '13 at 17:04

No, there is no direct equivalent in Delphi, there is something like this:

Student2:=StudentName.Create();
with Student2 do
begin
  FirstName:= 'Craig';
  LastName:= 'Playstead';
end;

MyObject:=TMyObject.Create();
With MyObject do
begin
    a:=1;
    b:=2;
end;
List.Add(MyObject);

// Although, there is something in Delphi that I haven't found in C++, Java or C#
With TMyObject.Create do
try
    // You can access TMyObject properties and method in here
finally
    Free;
end;

// For example:
With TMyModalForm.Create(Self) do
try
    if ShowModal() = mrOK then
    begin
        // etc
    end;
finally
    Free;
end;

A great example of 'with', although the keyword is [slightly dangerous.](http://stackoverflow.com/questions/514482/is-delphi-with-keyword-a-bad-practice) — David, Jul 21 '13 at 18:22

score 1 · Answer 3 · edited May 23 '17 at 12:00

1

You can override and reintroduce constructor Create. I'd recommend reading this fine answer here on StackOverflow.

edited May 23 '17 at 12:00

Community

1
1

answered Jul 21 '13 at 10:36

That isn't what the question asks. This doesn't need any special help from the class being initialised in C#. – Jul 21 '13 at 10:52
i know what constructor do my friend, actually my question is how to create object without declaring local variable and directly pass it to parameter argument like what i did in c# – vesal Jul 21 '13 at 11:16
3

I think what Mark means is that you can pass the parameters into the constructor, so have it all on a single line. @Mark, perhaps you could update your answer with more info? – David Jul 21 '13 at 18:21

score 1 · Answer 4 · answered Jul 21 '13 at 16:09

1

There is no equivalent syntax in Delphi. You must either reintroduce the constructor to add new parameters to it, or else construct the object first and then assign its members/properties as needed separately.

answered Jul 21 '13 at 16:09

Remy Lebeau

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initializing objects in delphi

4 Answers4