Compiler Hint: “Inline function '…' has not been expanded…”

Question

In a unit I use the function DeleteFile and the compiler outputs a hint:

\"H2443 Inline function \'DeleteFile\' has not been expanded because

Answer 1

Inline functions can be expanded inline. For example:

function AddPlus(const A,B: Integer): Integer; inline;
begin
  Result := A + B + 1;
end;

var
  x,y,z : Integer;
begin
  y := 22;
  z := 11;
  x := AddPlus(y, z);
end.

Is rewritten to:

var
  x,y,z : Integer;
begin
  y := 22;
  z := 11;
  x := y+z+1;
end.

This removes the overhead of a function call.

But in order to replace the call with the function body, the compiler needs more information, hence the complaint about the unit.

Beware that not all inline functions are converted. Some are treated just like normal functions (its up to the compiler). Besides, inline is only needed at really tight performance bottlenecks.