www.digitalmars.com         C & C++   DMDScript  

digitalmars.D - Standard struct constructors for the heap?

reply "bearophile" <bearophileHUGS lycos.com> writes:
Regarding the efforts of removing limitations from D, do you know 
if there are problems in implementing this oldish enhancement 
request?

http://d.puremagic.com/issues/show_bug.cgi?id=4086

The idea is to just allow the heap creation of simple structs 
with no need to define a constructor:


struct Node {
     int data;
     Node* next;
}
void main() {
     Node n1 = Node(10); // OK
     Node n2 = Node(10, null); // OK
}


I am writing many of those stupid struct initializations, it's 
boring busy work and they don't make the code more readable, just 
longer, so I'd like D to define them by itself:

this(int data_=int.init, Node* next_=(Node*).init)
pure nothrow  safe {
     this.data = data_;
     this.next = next_;
}

Removing this limit also makes D more uniform with 
locally-allocated struct construction semantics.

Bye,
bearophile
May 16 2012
next sibling parent reply "bearophile" <bearophileHUGS lycos.com> writes:
 struct Node {
     int data;
     Node* next;
 }
 void main() {
     Node n1 = Node(10); // OK
     Node n2 = Node(10, null); // OK
 }


Sorry, I meant:

struct Node {
     int data;
     Node* next;
}
void main() {
     Node n1 = new Node(10); // OK
     Node n2 = new Node(10, null); // OK
}

Bye,
bearophile
May 16 2012
parent reply "bearophile" <bearophileHUGS lycos.com> writes:
 struct Node {
     int data;
     Node* next;
 }
 void main() {
     Node n1 = new Node(10); // OK
     Node n2 = new Node(10, null); // OK
 }


I am sleepy. Third try:

struct Node {
     int data;
     Node* next;
}
void main() {
     Node* n1 = new Node(10); // OK
     Node* n2 = new Node(10, null); // OK
}
May 16 2012
parent reply Andrej Mitrovic <andrej.mitrovich gmail.com> writes:
On 5/17/12, bearophile <bearophileHUGS lycos.com> wrote:

 snip


Mixin workaround:

import std.conv;

 property string makeCtors(T)()
{
    T t;
    string res;
    foreach (i; 0 .. typeof(t.tupleof).length)
    {
        res ~= "this(typeof(this.tupleof[0.."
                ~ to!string(i+1)
                ~ "]) tup) { this.tupleof[0.."
                ~ to!string(i+1) ~ "] = tup; }\n";
    }

    return res;
}

struct Node
{
    mixin(makeCtors!Node);
    int data;
    Node* next;
}

void main() {
    Node* n1 = new Node(10); // OK
    Node* n2 = new Node(10, null); // OK
}
May 16 2012
parent "bearophile" <bearophileHUGS lycos.com> writes:
Andrej Mitrovic:


 Mixin workaround:


Yeah, in some cases I have used a similar workaround. Now I'd 
like to avoid the workaround.

Bye,
bearophile
May 17 2012
prev sibling parent "Steven Schveighoffer" <schveiguy yahoo.com> writes:
On Wed, 16 May 2012 19:50:25 -0400, bearophile <bearophileHUGS lycos.com>  
wrote:


 Regarding the efforts of removing limitations from D, do you know if  
 there are problems in implementing this oldish enhancement request?

 http://d.puremagic.com/issues/show_bug.cgi?id=4086


Should be absolutely feasible.

I'd also like to see this work:

struct X
{
    int x;
    this(int x) {this.x = x;}
}

void main(){
   X x; // no ctor needed
   X *xp = new X; // but this is an error!
}

-Steve
May 17 2012