[Issue 7753] Support opIndexCreate as part of index operator overloading in user-defined types

[d-bugmail]

http://d.puremagic.com/issues/show_bug.cgi?id=7753


Dmitry Olshansky <dmitry.o...@gmail.com> changed:

           What    |Removed                     |Added
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                 CC|                            |dmitry.o...@gmail.com


--- Comment #1 from Dmitry Olshansky <dmitry.o...@gmail.com> 2012-03-23 
03:28:52 PDT ---
It might be a good thing, but ...
Why not just return a proxy type upon each indexing?
The proxy type will have createIndex that will forward to others in turn.

Here a prof of concept I belive it could be generalized and polished.
For simplicity sake it's for n-dim arrays:

import std.stdio, std.exception;

struct Proxy(T)
{
        T* _this;
        int idx;
        void opAssign(X)(X value){
                    debug writeln("Proxy.opAssign"); 
            createIndex(idx) = value;            
        }
    static if(typeof(*_this).dimension >= 2)
    {

        // somewhere io expression ...a[idx][jdx]... is create all, except last
one
                auto opIndex(int jdx){
            return proxy(&_this.createIndex(idx), jdx);
        }
            //a[idx][jdx] = y; is create if non-existent
                auto opIndexAssign(X)(X val, int jdx){  //TODO: constraints!
            debug writeln("Proxy.opIndexAssign");
            _this.createIndex(idx).createIndex(jdx) = val;
        }
    }

        @property ref expr(){
                    debug writeln("Proxy.expr"); 
            return _this.normalIndex(idx);
        }

        alias expr this;
}

auto proxy(T)(T* x, int idx){ return Proxy!(T)(x,idx); }



struct M(size_t dim)
{
    static if(dim == 1){
        alias int Val;
    }
    else{
        alias M!(dim-1) Val;
    }
    enum dimension = dim;


    Val[] arr;


    ref createIndex(int idx){
        debug writeln("Created ", typeof(this).stringof);
        if(arr.length < idx)
            arr.length = idx+1;
        return arr[idx];
    }
        ref normalIndex(int idx){
        debug writeln("Indexed ", typeof(this).stringof);
        return arr[idx];
    }
    auto opIndex(int idx){
        return Proxy!(M)(&this, idx);
    }
        alias arr this;
}

unittest{
    M!(3) d3arr;    
    d3arr[1][2] = [2, 3, 4];
    assert(d3arr[1][2][2] == 4);
    int[] x = d3arr[1][2];                                              
    assert(d3arr[1][2].length == 3); 
    assert(d3arr[1][1] == null); //inited 
    //booom used before explicit = 
    assert(collectException!Error(d3arr[2][2][1] + 1 == 1) !is null);
}

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