Initialization of returned managed types

[pyscripter 689]

I guess everyone knows this already, but I did find this Stackoverflow answer surprising.  Can you guess what is the message shown?

function DoSomething(SomeBoolean: Boolean) : string;
begin
    if SomeBoolean then
        Result := 'abc'
end;

procedure TForm1.Button1Click(Sender: TObject);
var
    xx: string;
begin
    xx := DoSomething(True);
    xx := DoSomething(False);
        ShowMessage(xx);
end;

Shouldn't the above deserve a compiler warning?

Edited October 13, 2020 by pyscripter

[Darian Miller 361]

It's a "feature" not a bug.  But, yes, I would love a compiler warning.

 

[David Heffernan 2345]

It all went downhill when Borland decided that function return values were actually var parameters. Which means that in the case of managed types they get initialized by the caller. 

 

A function return value really should have pass by value callee to caller semantics. 

[Der schöne Günther 316]

I don't have the source at hand, but Embarcadero said that is is "too difficult" to fix, because the initialization of that variable takes place in another compiler code part that actually doesn't know how the variable is used.

 

There is, however, absolutely no excuse that there is no compiler warning. Embarcadero itself stumbles upon these uninitialized return values. Here's an example: [RSP-18300] TJson.Format() outputs invalid JSON - Embarcadero Technologies

Edited October 14, 2020 by Der schöne Günther

[Stefan Glienke 2002]

Use Fixinsight. It catches those.

[A.M. Hoornweg 144]

On 10/14/2020 at 8:01 AM, Stefan Glienke said:

Use Fixinsight. It catches those.

Thanks for mentioning this, downloading now...