digitalmars.D.learn - Array operations, dynamic arrays and length
- ixid (11/11) Jun 30 2015 int[] a = [1,1,1,1];
- "Marc =?UTF-8?B?U2Now7x0eiI=?= <schuetzm gmx.net> (3/14) Jul 01 2015 Yes, clearly a bug. Please open a bug report at
- Alex Parrill (6/17) Jul 01 2015 I don't think this is a bug.
- "Marc =?UTF-8?B?U2Now7x0eiI=?= <schuetzm gmx.net> (19/23) Jul 01 2015 I _do_ think it's a bug. Compare:
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J Miller
(8/32)
Jul 01 2015
Bug. "c[] = a[]
b[]" produces "[]" for operators "-" and - Steven Schveighoffer (4/8) Jul 02 2015 This is not a bug. You need to allocate memory before you can write to
- "Marc =?UTF-8?B?U2Now7x0eiI=?= <schuetzm gmx.net> (4/14) Jul 02 2015 This particular part works as intended, but the other things
- Steven Schveighoffer (5/17) Jul 02 2015 Right, my point was to address an obvious misconception on how these
- "Marc =?UTF-8?B?U2Now7x0eiI=?= <schuetzm gmx.net> (1/1) Jul 02 2015 https://issues.dlang.org/show_bug.cgi?id=14759
int[] a = [1,1,1,1]; int[] b = [1,1,1,1]; int[] c; c[] = a[] - b[]; c.writeln; This outputs []. This feels wrong, it feels like something that should have exploded or set the length to 4. If the lengths of a and b are mismatched it throws an exception. It also throws an exception if a dynamic array is longer or a static array is not the same length but is happy when a dynamic array is shorter. Is this intended behaviour and if so why?
Jun 30 2015
"Marc =?UTF-8?B?U2Now7x0eiI=?= <schuetzm gmx.net> On Tuesday, 30 June 2015 at 22:37:34 UTC, ixid wrote:int[] a = [1,1,1,1]; int[] b = [1,1,1,1]; int[] c; c[] = a[] - b[]; c.writeln; This outputs []. This feels wrong, it feels like something that should have exploded or set the length to 4. If the lengths of a and b are mismatched it throws an exception. It also throws an exception if a dynamic array is longer or a static array is not the same length but is happy when a dynamic array is shorter. Is this intended behaviour and if so why?Yes, clearly a bug. Please open a bug report at https://issues.dlang.org/
Jul 01 2015
On Tuesday, 30 June 2015 at 22:37:34 UTC, ixid wrote:int[] a = [1,1,1,1]; int[] b = [1,1,1,1]; int[] c; c[] = a[] - b[]; c.writeln; This outputs []. This feels wrong, it feels like something that should have exploded or set the length to 4. If the lengths of a and b are mismatched it throws an exception. It also throws an exception if a dynamic array is longer or a static array is not the same length but is happy when a dynamic array is shorter. Is this intended behaviour and if so why?I don't think this is a bug. Since you don't initialize `c` to anything, it defaults to an empty slice. Array [] operations apply to each element of a slice, but `c` doesn't have any elements, so it does nothing. Change `int[] c;` to `int[] c = new int[4];` and it works.
Jul 01 2015
On Wednesday, 1 July 2015 at 19:09:36 UTC, Alex Parrill wrote:I don't think this is a bug. Since you don't initialize `c` to anything, it defaults to an empty slice. Array [] operations apply to each element of a slice, but `c` doesn't have any elements, so it does nothing.I _do_ think it's a bug. Compare: import std.stdio; void main() { int[] a = [1,1,1,1]; int[] b = [1,1,1,1]; int[] c; int[2] d; c[] = a[] - b[]; // works c.writeln; // [] d[] = a[] - b[]; // works d.writeln; // [0, 0] d[] = a[]; // throws! // object.Error (0): Array lengths don't match for copy: 4 != 2 } So, in the case of subtraction, it assigns only as many elements as the destination has, but for direct assignment, it throws an error. This is clearly inconsistent.
Jul 01 2015
On Wednesday, 1 July 2015 at 21:15:13 UTC, Marc Schütz wrote:On Wednesday, 1 July 2015 at 19:09:36 UTC, Alex Parrill wrote:Bug. "c[] = a[] <op> b[]" produces "[]" for operators "-" and "/", but "object.Error (0): Array lengths don't match for vector operation: 0 != 4" for operators "+" and "*". Wat. Oh, and to make things really confusing, "auto e = a[] - b[]" and "int[] e = a[] - b[]" both cause "Error: array operation a[] - b[] without destination memory not allowed". Using dmd 2.067.0.I don't think this is a bug. Since you don't initialize `c` to anything, it defaults to an empty slice. Array [] operations apply to each element of a slice, but `c` doesn't have any elements, so it does nothing.I _do_ think it's a bug. Compare: import std.stdio; void main() { int[] a = [1,1,1,1]; int[] b = [1,1,1,1]; int[] c; int[2] d; c[] = a[] - b[]; // works c.writeln; // [] d[] = a[] - b[]; // works d.writeln; // [0, 0] d[] = a[]; // throws! // object.Error (0): Array lengths don't match for copy: 4 != 2 } So, in the case of subtraction, it assigns only as many elements as the destination has, but for direct assignment, it throws an error. This is clearly inconsistent.
Jul 01 2015
On 7/1/15 8:36 PM, J Miller wrote:Oh, and to make things really confusing, "auto e = a[] - b[]" and "int[] e = a[] - b[]" both cause "Error: array operation a[] - b[] without destination memory not allowed". Using dmd 2.067.0.This is not a bug. You need to allocate memory before you can write to it. Automatic allocation doesn't happen in D. -Steve
Jul 02 2015
On Thursday, 2 July 2015 at 10:48:56 UTC, Steven Schveighoffer wrote:On 7/1/15 8:36 PM, J Miller wrote:This particular part works as intended, but the other things _are_ buggy.Oh, and to make things really confusing, "auto e = a[] - b[]" and "int[] e = a[] - b[]" both cause "Error: array operation a[] - b[] without destination memory not allowed". Using dmd 2.067.0.This is not a bug. You need to allocate memory before you can write to it. Automatic allocation doesn't happen in D.
Jul 02 2015
On 7/2/15 8:21 AM, "Marc =?UTF-8?B?U2Now7x0eiI=?= <schuetzm gmx.net>" wrote:On Thursday, 2 July 2015 at 10:48:56 UTC, Steven Schveighoffer wrote:Right, my point was to address an obvious misconception on how these statements work. Other languages happily will allocate a new array in such cases, D does not. -SteveOn 7/1/15 8:36 PM, J Miller wrote:This particular part works as intended, but the other things _are_ buggy.Oh, and to make things really confusing, "auto e = a[] - b[]" and "int[] e = a[] - b[]" both cause "Error: array operation a[] - b[] without destination memory not allowed". Using dmd 2.067.0.This is not a bug. You need to allocate memory before you can write to it. Automatic allocation doesn't happen in D.
Jul 02 2015
On Thursday, 2 July 2015 at 12:59:03 UTC, Steven Schveighoffer wrote:On 7/2/15 8:21 AM, "Marc =?UTF-8?B?U2Now7x0eiI=?= <schuetzm gmx.net>" wrote:I knew that automatic allocation doesn't happen, but I'm confused by the fact if you explicitly declare "c" with "int[] c;" and then assign "c[] = a[] * b[]", versus using "auto c = a[] * b[]", you get two different errors (array length mismatch vs no destination memory).On Thursday, 2 July 2015 at 10:48:56 UTC, Steven Schveighoffer wrote:Right, my point was to address an obvious misconception on how these statements work. Other languages happily will allocate a new array in such cases, D does not. -SteveOn 7/1/15 8:36 PM, J Miller wrote:This particular part works as intended, but the other things _are_ buggy.Oh, and to make things really confusing, "auto e = a[] - b[]" and "int[] e = a[] - b[]" both cause "Error: array operation a[] - b[] without destination memory not allowed". Using dmd 2.067.0.This is not a bug. You need to allocate memory before you can write to it. Automatic allocation doesn't happen in D.
Jul 02 2015
On Thursday, 2 July 2015 at 19:27:57 UTC, J Miller wrote:I knew that automatic allocation doesn't happen, but I'm confused by the fact if you explicitly declare "c" with "int[] c;" and then assign "c[] = a[] * b[]", versus using "auto c = a[] * b[]", you get two different errors (array length mismatch vs no destination memory).I find it confusing as well. For me it's about consistency of syntax. For instance, auto z = x+y works with numeric types, but the equivalent you use for arrays doesn't work. It just means one more thing to remember.
Jul 04 2015
https://issues.dlang.org/show_bug.cgi?id=14759
Jul 02 2015