QualityCentral

Public Report

Report From: Delphi-BCB/Compiler/Delphi/Anonymous Methods [ Add a report in this area ]

Report #: 103383

Status: Open

Anonymous methods can use for-loop counters without a warning - wierd debugging

Project: Delphi

Build #: 16.0.4358.45540

Version: 16.3

Submitted By: Andreas Hausladen

Report Type: Minor failure / Design problem

Date Reported: 2/13/2012 10:02:09 AM

Severity: Infrequently encountered problem

Last Updated: 3/20/2012 2:24:39 AM

Platform: All platforms

Internal Tracking #: 289930

Resolution: None (Resolution Comments)

Resolved in Build: : None

Duplicate of: None

Voting and Rating

Overall Rating: No Ratings Yet

0.00 out of 5

Total Votes: None

Description

An anonymous method can capture a for-loop counter what makes the counter a non-local variable (this usually isn't allowed). As a result the debugger jumps out of the loop and back into the loop with every iteration. The CPU View shows the source line "end;" of the method in the "loop" code.

Non-local variables aren't allowed to be used as a for-loop counter. (X1019) But anonymous methods circumvents this compiler rule.

I also saw that the compiler generated an "Int16 range check" for a Int32 loop counter instead of an overflow check if the counter was captured. But I wasn't able to reproduce this is in a simple example.

EAX contains an Int32 and not a Int16, but the compiler generated

005107E8 0500800000       add eax,$00008000
005107ED 3DFFFF0000       cmp eax,$0000ffff
005107F2 7605             jbe $005107f9
005107F4 E87345EFFF       call @BoundErr
005107F9 050080FFFF       add eax,$ffff8000

Steps to Reproduce:

1. Create a new Console Application
2. Replace the code with the following program
3. Set a breakpoint on the for-loop
4. Start and step over [F8] the loop for some time

Expected:
The current debugged line is within the loop

Actual:
The debugger jumps the the methods "end" and back into the loop.

program QC103383;

{$APPTYPE CONSOLE}

uses
  SysUtils;

procedure Test;
var
  I: Integer;
  P: TProc;
begin
  for I := 0 to 10 do // breakpoint here, step over
    Write;                // step over

  I := 0;
  P :=
    procedure
    begin
      Inc(I);
    end;
  P;
end; // why are we here, while we are in the for-loop?

begin
  Test;
end.

Workarounds

None

Attachment

None

Comments

None

Developer Tools

Database Tools