Delphi return value by reference

Question

In C++ I can write a function like this:

int test(params) { }

And the value returned is only a number (r-value). But it is also possibile to do this:

int& test(params) { }

In this case the function returns a "complete variable". This means that the returned value is not just a value like before but it is a complete variabile having both r-value and l-value.

Is this possibile in Delphi? The first function would be function test(params):integer; but what about the second?

I have seen something similar when I try to implement a parallel for loop. Look at here there is an &. Does it have the reference meaning? I wasnt able to find a good answer by myself.

The & is explained in the documentation here: docwiki.embarcadero.com/RADStudio/en/… Essentially it is used to "escape" reserved words — David Heffernan
– David Heffernan, Commented May 19, 2017 at 7:56
See also: Is the practice of returning a C++ reference variable, evil? — David Heffernan
– David Heffernan, Commented May 19, 2017 at 7:57
Thank you I didnt see that in the documentation. I am attending a C++ class and I wanted to do a comparison between delphi and c++ (and not java in this case ofc) so I was confused about the presence of & — Alberto Miola
– Alberto Miola, Commented May 19, 2017 at 8:01
Yes, finding that in the documentation is tricky. It's a case of you need to know what it means in order to be able to search for it! — David Heffernan
– David Heffernan, Commented May 19, 2017 at 8:08

Remy Lebeau · Accepted Answer · 2017-05-19 07:40:38Z

5

Delphi does not support return-by-reference semantics like C++ does. The only options available are either:

return a pointer:
```
function test(params): PInteger;
```

use a var or out output parameter:

procedure test(params; var output: Integer);

procedure test(params; out output: Integer);

answered May 19, 2017 at 7:40

Remy Lebeau

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7 Comments

Rudy Velthuis Over a year ago

But if you want to return a full value, please do not return pointers! The var/out solution is the best,

David Heffernan Over a year ago

@RudyVelthuis That blanket statement doesn't make much sense to me. Sometimes returning a reference is appropriate, sometimes it is not. It depends on what you are trying a achieve.

David Heffernan Over a year ago

@Remy var or out do not correspond to returning a reference. They correspond to passing in references.

Rudy Velthuis Over a year ago

@David: If a value or record must be returned, pointers are always a bad choice. Yes, it is a blanket statement, and if the pointer is just a pointer into to something that was passed in, it's fine, but generally, that is not the case. Generally, it is bad habit to return values through pointers.

David Heffernan Over a year ago

@Rudy You don't understand. If you want to return a reference, return a reference. If you want to return a value, return a value. The type is irrelevant. Sometimes you want to return a reference, sometimes a value. You can't make a blanket statement. If I want to allow the caller to modify some value that I own, returning a value doesn't get it done. And vice versa.

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