Re: Variadic function template

[Ali Çehreli]

On 07/05/2013 07:55 AM, ref2401 wrote:

I have a number of elements of type Data!int or Data!string,

class Data(TItem) {
     TItem _item;

     this(TItem item) {
         _item = item;
     }
}

which need to be packed into container Pack. Pack!int for Data!int and
Pack!string for Data!string respectively.

class Pack(TItem) {
     string _name
     TItem[] _items;

     this(string name, size_t numOfItems) {
         _name = name;
         _items = new TItem[numOfItems];
     }
}

I'd like to have a function taking variable number of arguments of type
Data!TItem that packs them into single container Pack!TItem, similar to
this:

Pack!int p1 = pack("package1", new Data!int(24), new Data!int(78),
    new Data!int(147));
Pack!int p2 = pack("package2", new Data!int(-7), new Data!int(0),
    new Data!int(18), new Data!int(99), ... , new Data!int(128));
Pack!string p3 = pack("text pack 1", new Data!string("text1"),
    new Data!string("text2"), new Data!string("text3"));

I've tried several things but none of them works:
1) pack!(TItem, P = Data!TItems...)(string name, P params) { ... }
// compilation error

2) pack(TItem)(string name, Data!TItem...) { ... }
// compilation error

3) pack!(P...)(string name, P params) { ... }
// compiles, but I don't know how to get the type of parameters passed in.
//also I need to somehow check that all elements in 'params' have the
same type Data!TItem

Please advise how to implement the function. Thanks.

class Data(TItem) {
    TItem _item;

    this(TItem item) {
        _item = item;
    }
}

class Pack(TItem) {
    string _name;           // Added semicolon
    Data!TItem[] _items;    // Changed to Data!TItem

    this(string name) {     // Removed numOfItems
        _name = name;
    }

    // Added add(). (Instead of this method, you can take the elements as a
    // constructor parameter.)
    void add(Data!TItem[] items...) {
        _items ~= items;
    }
}

Pack!TItem pack(TItem)(string name, Data!TItem[] items...)
{
    auto p = new Pack!TItem(name);
    p.add(items);
    return p;
}

void main()
{
    Pack!int p1 = pack("package1", new Data!int(24));

    Pack!int p2 = pack("package2", new Data!int(-7), new Data!int(0));

    Pack!string p3 = pack("text pack 1", new Data!string("text1"));
}

Ali