bugGNU Octave - Bugs: bug #55523, default argument of anonymous...


bug #55523: default argument of anonymous function is not bound to value of local variable

Submitted by:  None
Submitted on:  Sun 20 Jan 2019 08:25:07 AM UTC  
Category:  Interpreter Severity:  1 - Wish
Priority:  3 - Low Item Group:  Feature Request
Status:  Confirmed Assigned to:  None
Originator Name:  Originator Email:  -email is unavailable-
Open/Closed:  Open Release:  dev
Operating System:  GNU/Linux

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Tue 25 Feb 2020 07:23:40 PM UTC, comment #5: 

Since the segmentation fault is fixed in what will soon be released as version 6.1, I've lowered the severity and retitled the summary to the primary remaining missing feature, that anonymous functions with default arguments don't correctly capture the values of local variables.

Mike Miller <mtmiller>
Project Administrator
Sun 03 Feb 2019 03:32:18 PM UTC, comment #4: 

Adding jwe to the CC list.

The new refactoring of the symbol table and how functions are stored has stopped the segfaults reportedi in this bug report.  However, that is on the development branch which won't become Octave 6.1 for another year.  If there was an easy patch for 5.1 that would be nice.  Otherwise, I have dropped the priority to low since this is a

However, I still think the results of this example are incorrect

octave:11> a = 1;
octave:12> b = 2;
octave:13> %Segmentation fault
octave:13> fb_disp = @(a = b) disp(a);
octave:14> fb_disp();
error: 'b' undefined near line 2 column 17
error: called from

I would have thought that the variable 'b' would have been replaced with the value 2 when the anonymous function was defined.

In terms of compatibility, we don't need to worry.  Matlab doesn't even allow default arguments to anonymous functions.

Rik <rik5>
Project Administrator
Tue 22 Jan 2019 02:09:03 AM UTC, comment #3: 

Confirmed.  It is a corner case so this is unlikely to be fixed in time for the 5.0 release, but hopefully in the first bug fix release that follows it.

Rik <rik5>
Project Administrator
Sun 20 Jan 2019 08:36:10 AM UTC, comment #2: 

I attached a file containing test cases.

(file #46037)

Sun 20 Jan 2019 08:32:56 AM UTC, comment #1: 

Also printing a default argument results in segmentation fault:

a = 1;
b = 2;
%Segmentation fault
fb_disp = @(a = b) disp(a);

a = 1;
b = 2;
%Segmentation fault
fa_disp = @(a = 3) disp(a);

a = 1;
b = 2;
%Segmentation fault
fb_pr = @(a = b) printf("%d\n",a);

Sun 20 Jan 2019 08:25:07 AM UTC, original submission:  

When a default argument of an anonymous handle function is assigned a variable with the same name an error is shown. For example:

a = 1;
b = 2;

fb = @(a = b) a;

fa = @(a = a) a;

This behavior can be seen in nested functions:

function testfunction()

        a = 1;
        b = 2;

        function ret = fb(a = b)
                ret = a;

        function ret = fa(a = a)
                ret = a;

        disp(fb()); %Good
        disp(fa());        % error: 'a' undefined




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Attach Files:

Attached Files
file #46037:  bug55523.m added by None (1KiB - application/octet-stream - Test cases for the reported bug)


Depends on the following items: None found

Items that depend on this one: None found


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  • -email is unavailable- added by rik5
  • -email is unavailable- added by rik5 (Posted a comment)

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    Follow 9 latest changes.

    Date Changed by Updated Field Previous Value => Replaced by
    2020-02-25 mtmiller Severity3 - Normal => 1 - Wish
        Item GroupSegfault, Bus Error, etc. => Feature Request
        Summarysegfault when default argument of anonymous/nested function is the same name as argument => default argument of anonymous function is not bound to value of local variable
    2019-02-03 rik5 Priority5 - Normal => 3 - Low
        Carbon-Copy- => Added jwe
    2019-01-22 rik5 SummaryDefault argument of anonymous/nested function can't be assigned a variable with the same name => segfault when default argument of anonymous/nested function is the same name as argument
    2019-01-22 rik5 StatusNone => Confirmed
        Release4.4.0 => dev
    2019-01-20 None Attached File- => Added bug55523.m, #46037

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