Re: Supporting foreach (k, v; T.init) for a user-defined (container) type

[Ali Çehreli via Digitalmars-d-learn]

On 10/24/22 14:26, Per Nordlöw wrote:
What property of a container (type) `T` enables iteration as
```d
foreach (k, v; T.init)
{
     ...
}
```

? I thought it sufficed to define `T.byKeyValue` but its presence seem 
to have no effect.

Another option is to use range functions where front() returns a Tuple. 
We have an esoteric feature where a tuple expands automatically in 
foreach loops:

import std.typecons : tuple;
import std.conv : to;
import std.stdio : writeln;
import std.range : take;

struct S {
    size_t count;
    bool empty = false;

    auto front() {
        const key = count;
        const value = key.to!string;
        return tuple(key, value);    // <-- HERE
    }

    void popFront() {
        ++count;
    }
}

void main() {
    foreach (k, v; S.init.take(10))
    {
        writeln(k, ": ", v);
    }
}

Ali