Integer function result - "Value assigned to '[function name]' never used"

Question

I found a solution to extract the contents of a zip file by creating a DLL using Ole. I put my own touch on this function, but for some reason, the compiler complains that the function's result is never used...

library unzipper;

{
  title     : UnZip for InnoSetup
  version   : 1.0
  author    : Daniel P. Stasinski
  email     : [email protected]
  begin     : Fri Nov 22 17:31:33 MST 2013
  license   : None
}

uses
  Windows,
  SysUtils,
  ComObj;

const
  SHCONTCH_NOPROGRESSBOX = 4;
  SHCONTCH_AUTORENAME = 8;
  SHCONTCH_RESPONDYESTOALL = 16;
  SHCONTF_INCLUDEHIDDEN = 128;
  SHCONTF_FOLDERS = 32;
  SHCONTF_NONFOLDERS = 64;

  UNZIP_SUCCESS = 0;
  UNZIP_FAIL = -1;

function UnzipFile(ZipFile, TargetFolder: WideString): Integer; stdcall;
var
  shellobj: variant;
  ZipFileV, SrcFile: variant;
  TargetFolderV, DestFolder: variant;
  shellfldritems: variant;
begin
  Result:= UNZIP_FAIL;
  try
    shellobj := CreateOleObject('Shell.Application');
    ZipFileV := string(ZipFile);
    TargetFolderV := string(TargetFolder);
    SrcFile := shellobj.NameSpace(ZipFileV);
    DestFolder := shellobj.NameSpace(TargetFolderV);
    shellfldritems := SrcFile.Items;
    DestFolder.CopyHere(shellfldritems, SHCONTCH_NOPROGRESSBOX or SHCONTCH_RESPONDYESTOALL);
    Result:= UNZIP_SUCCESS;
  except
    on e: exception do begin
      Result:= GetLastError;
    end;
  end;
end;

exports
  UnzipFile;

begin

end.

It gives me the message...

[DCC Hint] Unzipper.dpr(35): H2077 Value assigned to 'UnzipFile' never used

This is coming from the first line of code in the function, which I'm initializing to a constant of -1 - which is my own error code if the entire function fails. I don't believe the compiler should be complaining about this, but I could be wrong. I always exterminate all compiler hints and warnings, but in this case, the compiler is more of a complainer.

Is this a fluke in the compiler, or is something wrong in the code?

Why would you choose to unzip this way when Delphi has built in libraries? And tpAbbrevia. And so on. And why would GetLastError be meaningful here? I see no reason to believe that. — David Heffernan

Ken White Ken White · Accepted Answer · 2014-02-02T00:33:08

The compiler is correct, and there's something wrong in the code. :-)

The function will either return UNZIP_SUCCESS if it works, or the result of GetLastError if an exception is raised. Therefore, the first assignment to Result is unnecessary - there is no path of execution that would cause UNZIP_FAIL to be returned.

Integer function result - "Value assigned to '[function name]' never used"

2 Answers