View Issue Details
| ID | Project | Category | View Status | Date Submitted | Last Update |
|---|---|---|---|---|---|
| 0034972 | FPC | Compiler | public | 2019-01-30 06:37 | 2020-12-29 15:00 |
| Reporter | Kai Burghardt | Assigned To | Jonas Maebe | ||
| Priority | normal | Severity | minor | Reproducibility | always |
| Status | resolved | Resolution | no change required | ||
| Product Version | 3.0.4 | ||||
| Summary | 0034972: usage of default-intrinsic does not trigger range checks | ||||
| Description | When default(ordinalType) is used as the sole factor of an expression in an assignment, no range checks are triggered. | ||||
| Steps To Reproduce | program rangesWithoutDefault(input, output, stderr); {$R+} type r = -1..-1; var i: r; begin i := default(r); writeLn(i); end. | ||||
| Tags | range checks | ||||
| Fixed in Revision | |||||
| FPCOldBugId | |||||
| FPCTarget | - | ||||
| Attached Files |
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default initializes the memory to zero's. but indeed you example shows that it is not in range in your case. So: confirmed, because the range check should execute. |
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Suggestion: `default(T)` as sole factor in an expression yields a compile-time error if the range excludes `0` (zero). Except: (In Extended Pascal:) For data types that have a defined default value. Todo: While one can already specify an initialization value in a `var`-section, it is not associated with the data type. I suggest to implement Extended Pascal’s “initial-state-specifier”, cf. http://www.pascal-central.com/docs/iso10206.pdf (§ 6.6, PDF page 63), which links a “default” value _with_ a data _type_. The attached program should compile then. rangesWithDefault.pas (234 bytes)
program rangesWithDefault(input, output, stderr);
{$mode extendedPascal}
{$R+}
type
negativeNumber = low(nativeInt)..-1 value -1;
var
sadNumber: negativeNumber;
begin
sadNumber := default(negativeNumber);
writeLn(sadNumber);
end.
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From https://www.freepascal.org/docs-html/rtl/system/default.html: "In essence, this is a block of memory that is zeroed out". In Delphi (Default is not documented by last Delphi), there is no range check even when used in the declaration section. |
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Yes, you’re right, Serge. (As for now) `default` zeroes out a memory block. My point is though, zeroing out a memory block isn’t necessarily what I associate with the English word “default”. In assembly language it’s the `.zero` directive. “Zero” sounds like zeroing out, that’s plausible. And to be fair, in most cases `default` will assign `0` too, but it isn’t necessarily correct, hence this very bug report. Assigning zero to a range that doesn’t include zero is wrong and should not be possible (but apparently is). In Pascal’s spirit we should prevent the programmer from doing stupid things. Assigning an invalid value to a variable is one such “stupid thing”. |
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A global variable will also be initialised with 0, even if that is not a valid value for that variable. The same goes for fields in a class. Default just is a way to be able to do this for any variable at any point. It is not guaranteed to be a valid value, but basically "make this variable uninitialised again". The Extended Pascal functionality would definitely be useful, but that's different from the (Delphi-originated) Default() intrinsic. |
| Date Modified | Username | Field | Change |
|---|---|---|---|
| 2019-01-30 06:37 | Kai Burghardt | New Issue | |
| 2019-01-30 06:37 | Kai Burghardt | Tag Attached: range checks | |
| 2019-02-01 15:49 | Thaddy de Koning | Note Added: 0113781 | |
| 2019-02-01 15:51 | Thaddy de Koning | Note Edited: 0113781 | View Revisions |
| 2020-04-27 22:01 | Kai Burghardt | Note Added: 0122474 | |
| 2020-04-27 22:01 | Kai Burghardt | File Added: rangesWithDefault.pas | |
| 2020-04-27 22:04 | Kai Burghardt | Note Edited: 0122474 | View Revisions |
| 2020-04-28 03:19 | Serge Anvarov | Note Added: 0122480 | |
| 2020-04-28 10:47 | Kai Burghardt | Note Added: 0122488 | |
| 2020-04-28 22:09 | Jonas Maebe | Note Added: 0122512 | |
| 2020-12-29 15:00 | Jonas Maebe | Assigned To | => Jonas Maebe |
| 2020-12-29 15:00 | Jonas Maebe | Status | new => resolved |
| 2020-12-29 15:00 | Jonas Maebe | Resolution | open => no change required |
| 2020-12-29 15:00 | Jonas Maebe | FPCTarget | => - |
