Re: [Challenge] implementing the ambiguous operator in D

[Simen kjaeraas]

Simen kjaeraas <simen.kja...@gmail.com> wrote:

I believe this will only work with arrays as input. Either that, or I need

a way to make this work:

struct Foo( R ) if ( isForwardRange!R ) {
     bool delegate( ElementType!R ) bar;
     Filter!( bar, R ) range;
}

Or, well, something like it. I need a static type for a Filter that
delegates to a struct member, in this case bar.

I would have thought this'd work, but apparently I'm wrong:


module foo;

import std.stdio;
import std.algorithm;
import std.range;

struct Foo( R ) if ( isForwardRange!R ) {
    R range;
    void delegate( ) _popFront;
    bool delegate( ) _empty;
    ElementType!R delegate( ) _front;

    this( R rng ) {
        range = rng;
        _popFront = { range.popFront( ); };
        _empty = { return range.empty; };
        _front = { return range.front; };
    }

    void attempt( bool delegate( ElementType!R ) dg ) {
        auto rng = filter!dg( range );
        _popFront = { rng.popFront( ); };
        _empty = { return rng.empty; };
        _front = { return rng.front; };
    }

    void popFront( ) {
        _popFront( );
    }

    @property
    bool empty( ) {
        return _empty( );
    }

    @property
    ElementType!R front( ) {
        return _front( );
    }
}

Foo!R bar( R )( R rng ) if ( isForwardRange!R ) {
    return Foo!R( rng );
}

void main() {
    auto b = bar( [1,2,3] );
    foreach ( e; b ) {
        writeln( e );
    }
}



Output:
1
object.Error: Access Violation

--
Simen