Is the [Ref] attribute for const record parameters useful?

Question

With the latest Delphi version (Berlin/10.1/24), is the [Ref] attribute really necessary?

I ask this because the online doc says:

Constant parameters may be passed to the function by value or by reference, depending on the specific compiler used. To force the compiler to pass a constant parameter by reference, you can use the [Ref] decorator with the const keyword.

You may find the answer here: Can I force const to pass by reference (aka the missing in parameter). — LU RD
That is, const records <= SizeOf(pointer) are passed by value. If you want to ensure that a reference is passed, use the [ref] attribute. — LU RD
ok that sounds very sensible, and makes me think I can give up on using the Ref attribute for const record parameters. — user3942667

David Heffernan David Heffernan · Accepted Answer · 2016-12-02T10:07:37

It's pretty much as described by the documentation. You'd use [ref] if you had a reason to enforce the argument to be passed by reference. One example that I can think of is for interop. Imagine you are calling an API function that is defined like this:

typedef struct {
    int foo;
} INFO;

int DoStuff(const INFO *lpInfo);

In Pascal you might wish to import it like this:

type
  TInfo = record
    foo: Integer;
  end;

function DoStuff(const Info: TInfo): Integer; cdecl; external libname;

But because TInfo is small, the compiler might choose to pass the structure by value. So you can annotate with [ref] to force the compiler to pass the parameter as a reference.

function DoStuff(const [ref] Info: TInfo): Integer; cdecl; external libname;

Is the [Ref] attribute for const record parameters useful?

2 Answers