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digitalmars.D.bugs - [Issue 6174] New: Initialize const fixed-size array in constructor

reply d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=6174

           Summary: Initialize const fixed-size array in constructor
           Product: D
           Version: D2
          Platform: x86
        OS/Version: Windows
            Status: NEW
          Severity: enhancement
          Priority: P2
         Component: DMD
        AssignedTo: nobody puremagic.com
        ReportedBy: bearophile_hugs eml.cc


--- Comment #0 from bearophile_hugs eml.cc 2011-06-18 04:31:54 PDT ---
This program shows that you are allowed to initialize a single const char
inside static this() and struct constructor, but you are not allowed to
initialize the items of a char array:


const char gc;
const char[1] ga;
static this() {
    gc = 'a';    // OK
    ga[0] = 'a'; // line 5, Err
}
struct Foo {
    const char cc;
    const char[1] array;
    this(char c) {
        cc = c;       // OK
        array = [c];  // line 12, Err
        array[0] = c; // line 12, Err
    }
}
void main() {}


DMD 2.053:
temp.d(5): Error: ga[0] isn't mutable
temp.d(12): Error: slice this.array[] is not mutable
temp.d(13): Error: this.array[0] isn't mutable

I'd like to initialize the arrays too.

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Jun 18 2011
next sibling parent d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=6174


Trass3r <mrmocool gmx.de> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |rejects-valid
                 CC|                            |mrmocool gmx.de
           Platform|x86                         |All
         OS/Version|Windows                     |All
           Severity|enhancement                 |normal


--- Comment #1 from Trass3r <mrmocool gmx.de> 2011-08-24 17:19:30 PDT ---
This also happens without explicit slicing/indexing:

immutable float[3] foo;

static this()
{
    foo = [1,2,3];
}

In my actual code I need a function to initialize the array.
It uses exp and thus isn't CTFEable. Hence static this would be the only to
initialize this immutable.

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prev sibling next sibling parent d-bugmail puremagic.com writes:
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--- Comment #3 from bearophile_hugs eml.cc 2011-11-09 19:29:02 PST ---
See also a comment by Kenji Hara:

http://www.digitalmars.com/webnews/newsgroups.php?art_group=digitalmars.D&article_id=148428


 Inside constructor, compiler can detect that this.a[n] is part of the
 fields of 'this' (because static array is value type), then should
 allow to bypass const type checking for assignment.
 But dynamic array and associative array are reference type, then
 compiler cannot detect that the elements of them (this.b[n] and
 this.aa[key]) are part of 'this'. Therefore line 8 and 9 cannot bypass
 const type checking, even if inside constructor, then should be
 rejected.
 
 I have call this concept "transitively modifiable", and I have
 implemented it with dmd/pull/166.
 "Transitively modifiable" is only checked inside constructor, and
 allow more flexible initializing.
 I think this is reasonable improvement.



So all this is expected to eventually compile and run:


const struct Foo1 {
    const int[1] a;
    this(in int x) pure {
        a[0] = x; // Error
    }
}
const struct Foo2 {
    const int[1] a;
    this(in int x) pure {
        a = [x]; // Error
    }
}
const struct Foo3 {
    const int[1] a;
    this(in int x) pure {
        a[] = x; // Error
    }
}
const struct Foo4 {
    const int a;
    this(in int x) pure {
        a = x; // OK
    }
}
void main() {}

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

While this is not yet compilable:


const struct Foo {
    const int[] a;
    const int[int] aa;
    this(in int n) pure {
        this.a = new int[5];
        this.a[0] = n; // line 6
        this.aa[1] = 2; // line 7
    }
}
void main() {}


test.d(6): Error: this.a[0] isn't mutable
test.d(7): Error: this.aa[1] isn't mutable

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prev sibling next sibling parent d-bugmail puremagic.com writes:
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--- Comment #4 from Kenji Hara <k.hara.pg gmail.com> 2011-11-12 06:56:29 PST ---
*** Issue 6924 has been marked as a duplicate of this issue. ***

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prev sibling next sibling parent d-bugmail puremagic.com writes:
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hsteoh quickfur.ath.cx changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |hsteoh quickfur.ath.cx


--- Comment #5 from hsteoh quickfur.ath.cx 2012-04-09 19:42:42 PDT ---
*** Issue 7882 has been marked as a duplicate of this issue. ***

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prev sibling next sibling parent d-bugmail puremagic.com writes:
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yebblies <yebblies gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
                 CC|                            |yebblies gmail.com
         Resolution|                            |FIXED


--- Comment #6 from yebblies <yebblies gmail.com> 2012-10-08 05:48:48 EST ---
https://github.com/D-Programming-Language/dmd/commit/5b42e51481d186ee5e3c2684a237a05cea33a0cf

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--- Comment #7 from bearophile_hugs eml.cc 2012-10-07 13:01:14 PDT ---
This is an improvement of D.


std.algorithm.copy can't be used to initialize const array fields, but this is
not important:


import std.algorithm: copy;
class Foo {
    const int[3] bar;
    this() {
        auto data = [10, 20, 30];
        foreach (i, d; data) bar[i] = d; // OK
        copy(data, bar[]); // error
    }
}
void main() {}

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--- Comment #8 from bearophile_hugs eml.cc 2012-10-07 13:12:27 PDT ---
Is this expected? Do you want me to put this in a new bug report?


struct Foo {
    int[1] bar;
}
const Foo[1] foos;
static this() {
    foreach (i; 0 .. foos.length)
        foos[i].bar[i] = 1; // OK
    foreach (i, ref f; foos)
        f.bar[i] = 1; // Error
}
void main() {}

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--- Comment #9 from Kenji Hara <k.hara.pg gmail.com> 2012-10-08 05:35:43 PDT ---
(In reply to comment #8)

 Is this expected? Do you want me to put this in a new bug report?
 
 struct Foo {
     int[1] bar;
 }
 const Foo[1] foos;
 static this() {
     foreach (i; 0 .. foos.length)
         foos[i].bar[i] = 1; // OK
     foreach (i, ref f; foos)
         f.bar[i] = 1; // Error
 }
 void main() {}


Hmm, it's interesting. The accessed memory through the reference 'f' would
specify a part of the constructed fields, and compiler would be able to detect
it in statically.

Please put in a new report.

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--- Comment #10 from bearophile_hugs eml.cc 2012-10-08 10:22:27 PDT ---
(In reply to comment #9)


 Please put in a new report.


OK, Issue 8783
Thank you.

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prev sibling parent d-bugmail puremagic.com writes:
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--- Comment #11 from github-bugzilla puremagic.com 2013-01-31 01:47:44 PST ---
Commit pushed to master at https://github.com/D-Programming-Language/dmd

https://github.com/D-Programming-Language/dmd/commit/aa33955a6ed38ab64df903b2298988f9cde42914
Clean up test cases for issue 6174

Merged similar tests by making them parameterize.

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