• mark (31/31) Mar 09 2020 I have this struct:
• Steven Schveighoffer (7/47) Mar 09 2020 aa.dup. However, this isn't going to work in a const member function
• mark (9/15) Mar 09 2020 [snip]
• Steven Schveighoffer (8/26) Mar 09 2020 Right, because it's inside a const member function, the tags member is

mark <mark qtrac.eu> writes:

I have this struct:

struct Deb {
     string name;
     ...
     Unit[string] tags; // set of tags

     Deb copy() const {
         Deb deb;
         ...
         foreach (key, value; tags) // XXX
             deb.tags[key] = value;
         return deb;
     }

     void clear() {
         name = "";
         ...
         tags.clear;
     }

...
}

I am populating an AA with these structs:

Deb[string] debForName;

I'm using this approach (pseudo-code):

Deb deb;
foreach (datum; data) {
     populateDeb(datum, deb);
     debForName[deb.name] = deb.copy; // YYY
     deb.clear;
}

(1) XXX Is there a nicer way to copy an AA?
(2) YYY Is there a nicer way to copy a struct? Use a copy 
constructor or implement a dup or idup?

Steven Schveighoffer <schveiguy gmail.com> writes:

On 3/9/20 9:23 AM, mark wrote:
 I have this struct:
 
 struct Deb {
      string name;
      ...
      Unit[string] tags; // set of tags
 
      Deb copy() const {
          Deb deb;
          ...
          foreach (key, value; tags) // XXX
              deb.tags[key] = value;
          return deb;
      }
 
      void clear() {
          name = "";
          ...
          tags.clear;
      }
 
 ....
 }
 
 I am populating an AA with these structs:
 
 Deb[string] debForName;
 
 I'm using this approach (pseudo-code):
 
 Deb deb;
 foreach (datum; data) {
      populateDeb(datum, deb);
      debForName[deb.name] = deb.copy; // YYY
      deb.clear;
 }
 
 (1) XXX Is there a nicer way to copy an AA?

aa.dup. However, this isn't going to work in a const member function 
(though technically there shouldn't be anything wrong with it).

 (2) YYY Is there a nicer way to copy a struct? Use a copy constructor or 
 implement a dup or idup?

I would name it dup instead of copy for consistency with D. A copy 
constructor is pretty heavy for a struct to do a complete duplication of 
the AA. You should have to opt-in to that.

-Steve

mark <mark qtrac.eu> writes:

On Monday, 9 March 2020 at 14:45:15 UTC, Steven Schveighoffer 
wrote:
 On 3/9/20 9:23 AM, mark wrote:
 I have this struct:


[snip]
 I would name it dup instead of copy for consistency with D. A 
 copy constructor is pretty heavy for a struct to do a complete 
 duplication of the AA. You should have to opt-in to that.

 -Steve

Thanks, I'd already realised I ought to rename it .dup.

Also, I only actually need to create it from the keys since I'm 
using the tags AA as a set so every value is the same. I did try 
tags.dup but got this:

src/deb.d(25,24): Error: cannot implicitly convert expression 
dup(this.tags) of type const(void[0])[string] to void[0][string]

Steven Schveighoffer <schveiguy gmail.com> writes:

On 3/9/20 11:49 AM, mark wrote:
 On Monday, 9 March 2020 at 14:45:15 UTC, Steven Schveighoffer wrote:
 On 3/9/20 9:23 AM, mark wrote:
 I have this struct:


 [snip]
 I would name it dup instead of copy for consistency with D. A copy 
 constructor is pretty heavy for a struct to do a complete duplication 
 of the AA. You should have to opt-in to that.

 
 Thanks, I'd already realised I ought to rename it .dup.
 
 Also, I only actually need to create it from the keys since I'm using 
 the tags AA as a set so every value is the same. I did try tags.dup but 
 got this:
 
 src/deb.d(25,24): Error: cannot implicitly convert expression 
 dup(this.tags) of type const(void[0])[string] to void[0][string]
 

Right, because it's inside a const member function, the tags member is 
const.

Right now, it looks like dup does not work even for value types (e.g. 
const int[int] -> int[int]) let alone types with indirection (it should 
also work for string keys). If there's not an issue already, someone 
should file it.

-Steve