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digitalmars.D.bugs - [Issue 7444] New: Require [] for array copies too

reply d-bugmail puremagic.com writes:
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           Summary: Require [] for array copies too
           Product: D
           Version: D2
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: enhancement
          Priority: P2
         Component: DMD
        AssignedTo: nobody puremagic.com
        ReportedBy: bearophile_hugs eml.cc


--- Comment #0 from bearophile_hugs eml.cc 2012-02-05 11:10:57 PST ---
This is derived from issue 3971 see there for more (messy) discussions.

In 2.058 this compiles:


int[100] foo() {
    int[100] a;
    return a;
}
void main() {
    int[10_000] a, b;
    auto c = new int[10_000];
    a = 1;
    a = b;
    a = c;
    auto d = foo();
}


But for consistency of the vector ops syntax, and to help the programmer spot
where the code is doing a potentially long copy, I suggest to turn that first
program into a compile-time error, and require [] on lvalues everywhere you
perform a vector operation, like when you copy a int[N] on another int[N], etc:


int[100] foo() {
    int[100] a;
    return a;
}
void main() {
    int[10_000] a, b;
    auto c = new int[10_000];
    a[] = 1;
    a[] = b;
    a[] = c;
    auto d[] = foo(); // currently an error
}

- - - - - - - - - - - - - - - -

But note that normally all array ops require a [] even on the rvalue:


void main() {
    int[10_000] a, b;
    a[] += b[];
}



So an alternative stricter proposal is to require [] on the right too:


int[100] foo() {
    int[100] a;
    return a;
}
void main() {
    int[10_000] a, b;
    auto c = new int[10_000];
    auto d = new int[10_000];
    a[] = 1;
    a[] = b[];
    a[] = c[];
    c[] = d[];
    auto e[] = foo()[]; // currently an error
}



It helps the programmer tell apart two different cases, that currently are
usable with the same syntax (from an example by Don):


void main() {
    int[][3] x;
    int[]    y;
    int[]    z;

    x[] = z; // copies just the z pointer
    y[] = z; // copies the elements in z
}



Requiring [] on the right (rvalue) for the copy of many items avoids the
ambiguity:

void main() {
    int[][3] x;
    int[]    y;
    int[]    z;
    x[] = z;
    y[] = z[];
}

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timon.gehr gmx.ch changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |timon.gehr gmx.ch


--- Comment #1 from timon.gehr gmx.ch 2012-02-05 15:34:04 PST ---
While I agree that the syntax should be enforced more strictly in general, I
still completely disagree with requiring [] on static array copies. Static
arrays are value types of fixed size, and should be treated as such. Requiring
[] is just wrong.

void foo(int[4] x){}
void foo(int[] y){}

void main(){
    int[4] x, y;
    struct S{int[4] x;}
    S a, b;
    x = y;
    a = b; // why should this work if the above does not?
    foo(x);   // copies, you want this to be an error
    foo(x[]); // calls the other overload, does not copy
}

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--- Comment #2 from Kenji Hara <k.hara.pg gmail.com> 2012-02-09 05:33:52 PST ---
(In reply to comment #1)
 While I agree that the syntax should be enforced more strictly in general, I
 still completely disagree with requiring [] on static array copies. Static
 arrays are value types of fixed size, and should be treated as such. Requiring
 [] is just wrong.
 
 void foo(int[4] x){}
 void foo(int[] y){}
 
 void main(){
     int[4] x, y;
     struct S{int[4] x;}
     S a, b;
     x = y;
     a = b; // why should this work if the above does not?
     foo(x);   // copies, you want this to be an error
     foo(x[]); // calls the other overload, does not copy
 }

I completely agree with Timon. When x and y are declared with same type T, x = y is identity assignment, and it is valid syntax even if T is static array type. -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------
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--- Comment #3 from Kenji Hara <k.hara.pg gmail.com> 2012-02-09 06:31:34 PST ---
I'd like to provide an exhaustive test that should compile after fixing the
enhancement suggested by me and timon.

----
// X: Changed accepts-invalid to rejects-invalid by this issue
// a: slice assginment
// b: element-wise assignment

static assert(!__traits(compiles, { sa   = e; }));      // X
static assert( __traits(compiles, { sa[] = e; }));      // b
static assert(!__traits(compiles, { da   = e; }));
static assert( __traits(compiles, { da[] = e; }));      // b

// lhs is static array
static assert( __traits(compiles, { sa   = sa;   }));   // b == identity assign
static assert(!__traits(compiles, { sa   = sa[]; }));   // X
static assert(!__traits(compiles, { sa[] = sa;   }));   // X
static assert( __traits(compiles, { sa[] = sa[]; }));   // b

static assert(!__traits(compiles, { sa   = da;   }));   // X
static assert(!__traits(compiles, { sa   = da[]; }));   // X
static assert( __traits(compiles, { sa[] = da;   }));   // b
static assert( __traits(compiles, { sa[] = da[]; }));   // b

// lhs is dynamic array
static assert(!__traits(compiles, { da   = sa;   }));   // X
static assert( __traits(compiles, { da   = sa[]; }));   // a
static assert(!__traits(compiles, { da[] = sa;   }));   // X
static assert( __traits(compiles, { da[] = sa[]; }));   // b

static assert( __traits(compiles, { da   = da;   }));   // a == identity assign
static assert( __traits(compiles, { da   = da[]; }));   // a
static assert( __traits(compiles, { da[] = da;   }));   // b
static assert( __traits(compiles, { da[] = da[]; }));   // b
----

bearophile says that sa = sa should be rejected and must replace it to sa[] =
sa[].
But I and timon disagree it.

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--- Comment #4 from timon.gehr gmx.ch 2012-02-09 07:01:17 PST ---
Maybe sa[] = da and da[] = da should be '// X' too.

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Kenji Hara <k.hara.pg gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |pull


--- Comment #5 from Kenji Hara <k.hara.pg gmail.com> 2012-02-10 04:23:32 PST ---
(In reply to comment #4)
 Maybe sa[] = da and da[] = da should be '// X' too.

Hmm, OK. If it is an element-wise assignment, we should add explicit slicing both side of AssignExp. I've posted a pull to implement this enhancement: https://github.com/D-Programming-Language/dmd/pull/702 Updated test: https://github.com/D-Programming-Language/dmd/pull/702/files#L6R250 -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------
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Walter Bright <bugzilla digitalmars.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |bugzilla digitalmars.com


--- Comment #6 from Walter Bright <bugzilla digitalmars.com> 2012-02-17
23:27:14 PST ---
The enhancement is to disallow:

  sa = da; // use sa[] = da[] instead
  sa = e;  // use sa[] = e instead

I'm not sure this is worth the existing code breakage.

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--- Comment #7 from bearophile_hugs eml.cc 2012-02-18 05:02:07 PST ---
(In reply to comment #6)

 I'm not sure this is worth the existing code breakage.

I thin it's worth it, if you want with warning / deprecation / error stages. But if want, I'll ask for a little voting in the main D newsgroup. -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------
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--- Comment #8 from bearophile_hugs eml.cc 2012-02-22 16:07:54 PST ---
See why a consistent syntax matters: Issue 7564

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--- Comment #9 from github-bugzilla puremagic.com 2012-10-14 19:19:00 PDT ---
Commits pushed to master at https://github.com/D-Programming-Language/druntime

https://github.com/D-Programming-Language/druntime/commit/a77c82772e7e7b2d1d863b1fb56b614b9d4bc6a1
fix Issue 7444 - Require [] for array copies too

https://github.com/D-Programming-Language/druntime/commit/be3a7fa1bc726b453203c058ff2fa8c81dcfcab1
Merge pull request #314 from 9rnsr/fix7444

Supplemental changes for Issue 7444 - Require [] for array copies too

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--- Comment #10 from github-bugzilla puremagic.com 2012-11-20 09:55:06 PST ---
Commits pushed to master at https://github.com/D-Programming-Language/phobos

https://github.com/D-Programming-Language/phobos/commit/28dedee456e741f02f08a944f41daa9e46236224
Issue 7444 - Require [] for array copies too

https://github.com/D-Programming-Language/phobos/commit/9a6dad8a2ac5841bdcfa2b86082450818f6eefab
Merge pull request #960 from 9rnsr/fix7444

Supplemental changes for Issue 7444 - Require [] for array copies too

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--- Comment #11 from github-bugzilla puremagic.com 2012-11-21 20:12:48 PST ---
Commits pushed to master at https://github.com/D-Programming-Language/druntime

https://github.com/D-Programming-Language/druntime/commit/e5895640c83d8b5b4c8b2404b4e639ba6fdf2243
Additional fix Issue 7444 in Posix platforms

https://github.com/D-Programming-Language/druntime/commit/a54f41c98aa26eeb70274e8b78d8abfb575bcebc
Merge pull request #352 from 9rnsr/fix7444

Additional fix Issue 7444 in Posix platforms

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--- Comment #12 from github-bugzilla puremagic.com 2013-03-06 22:53:51 PST ---
Commits pushed to master at https://github.com/D-Programming-Language/dmd

https://github.com/D-Programming-Language/dmd/commit/57b770ed49379c5af726d23356e0f75818a3f859
Issue 7444 - Require [] for array copies too

https://github.com/D-Programming-Language/dmd/commit/ba1009c5561b51b8f18d9c869fde9bd45cb7ebc7
Merge pull request #702 from 9rnsr/fix7444

Issue 7444 - Require [] for array copies too

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--- Comment #13 from bearophile_hugs eml.cc 2013-03-07 04:22:27 PST ---
(In reply to comment #12)
 Commits pushed to master at https://github.com/D-Programming-Language/dmd
 
 https://github.com/D-Programming-Language/dmd/commit/57b770ed49379c5af726d23356e0f75818a3f859
 Issue 7444 - Require [] for array copies too
 
 https://github.com/D-Programming-Language/dmd/commit/ba1009c5561b51b8f18d9c869fde9bd45cb7ebc7
 Merge pull request #702 from 9rnsr/fix7444
 
 Issue 7444 - Require [] for array copies too

I have tried this change, and now the first test case of this ER: int[100] foo() { int[100] a; return a; } void main() { int[10_000] a, b; auto c = new int[10_000]; a = 1; a = b; a = c; auto d = foo(); } gives a ICE: temp.d(8): Warning: explicit element-wise assignment (a)[] = 1 is better than a = 1 temp.d(10): Warning: explicit element-wise assignment (a)[] = (c)[] is better than a = c Assertion failure: '0' on line 1193 in file 'glue.c' -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------
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--- Comment #14 from bearophile_hugs eml.cc 2013-03-07 04:58:19 PST ---
(In reply to comment #13)

 gives a ICE:

Smaller test case: void main() { int[1] a; a = 1; } -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------
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--- Comment #15 from Kenji Hara <k.hara.pg gmail.com> 2013-03-07 05:14:27 PST
---
(In reply to comment #14)
 (In reply to comment #13)
 
 gives a ICE:

Smaller test case: void main() { int[1] a; a = 1; }

What version and compiler switch do you use? I cannot reproduce the ICE. -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------
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--- Comment #16 from bearophile_hugs eml.cc 2013-03-07 12:10:52 PST ---
(In reply to comment #15)

 What version and compiler switch do you use? I cannot reproduce the ICE.

I am using the GIT head compiler, I have downloaded and compiled dmd few hours ago, after this patch was merged. I am on Windows 32 bit, and I have compiled the code with: dmd -wi test.d -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------
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--- Comment #17 from Kenji Hara <k.hara.pg gmail.com> 2013-03-07 15:41:56 PST
---
(In reply to comment #16)
 (In reply to comment #15)
 
 What version and compiler switch do you use? I cannot reproduce the ICE.

I am using the GIT head compiler, I have downloaded and compiled dmd few hours ago, after this patch was merged. I am on Windows 32 bit, and I have compiled the code with: dmd -wi test.d

Thanks. -w option does not reproduce it, but -wi does. -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------
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Kenji Hara <k.hara.pg gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|                            |FIXED


--- Comment #18 from Kenji Hara <k.hara.pg gmail.com> 2013-03-07 17:00:31 PST
---
(In reply to comment #17)
 (In reply to comment #16)
 (In reply to comment #15)
 
 What version and compiler switch do you use? I cannot reproduce the ICE.

I am using the GIT head compiler, I have downloaded and compiled dmd few hours ago, after this patch was merged. I am on Windows 32 bit, and I have compiled the code with: dmd -wi test.d

Thanks. -w option does not reproduce it, but -wi does.

OK, I opened a new report bug 9663 for the regression. -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------
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Walter Bright <bugzilla digitalmars.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|FIXED                       |WONTFIX


--- Comment #19 from Walter Bright <bugzilla digitalmars.com> 2013-10-20
09:38:57 PDT ---
This pull:

https://github.com/D-Programming-Language/dmd/pull/2673

undoes it with explanation. Reclassified as "wontfix".

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--- Comment #20 from bearophile_hugs eml.cc 2013-10-20 10:49:58 PDT ---
(In reply to comment #19)
 This pull:
 
 https://github.com/D-Programming-Language/dmd/pull/2673
 
 undoes it with explanation. Reclassified as "wontfix".

What? After all the energy time and work spent on fixing this problem!? If you take a look at the patch by Kenji you see: - else if (global.params.warnings && !global.gag && op == TOKassign && + else if (0 && global.params.warnings && !global.gag && op == TOKassign && That means the code is commented out, but it's meant to be activated back in dmd 2.065 to try to fix this issue better. I will probably re-open this issue later. -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------
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bearophile_hugs eml.cc changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|RESOLVED                    |REOPENED
         Resolution|WONTFIX                     |


--- Comment #21 from bearophile_hugs eml.cc 2013-10-20 12:29:43 PDT ---
Reopened, this will wait for dmd 2.065, to see if Kenji or others are able to
find a solution. If no solution will be found, we'll close this again.

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