Mixin - to get to the content-type `MapResult!(__lambda1, int[]).MapResult`

[Dennis Ritchie via Digitalmars-d-learn]

On Saturday, 30 May 2015 at 23:58:44 UTC, Ali Çehreli wrote:
> On 05/30/2015 12:19 PM, Dennis Ritchie wrote:
>
> First, unfortunately, I don't understand you completely. Sorry 
> about that... :)

Nothing to worry about! Now you will understand me till the 
end... :)

> Regarding that, the intermediate range.front is already 
> available right before the .walk part. You can do anything at 
> that point. There was some proposals about a 'tap' algorithm 
> that could be used for debugging purposes. Here is a quick 
> implementation:

Yes, it is an intermediate stage of code that will help me to 
explain what I want to get.

> import std.stdio, std.algorithm;
>
> static int idx;
>
> void walk(R)(R range) {
>     while (!range.empty) {
>         range.front;
>         range.popFront;
>     }
> }
>
> struct Tap(alias func, R)
> {
>     R range;
>
>     alias range this;
>
>     @property auto front()
>     {
           func(range.front); // It's a necessary part of the 
code! :)
>         return range.front;
>     }
> }
>
> auto tap(alias func, R)(R range)
> {
>     return Tap!(func, R)(range);
> }
>
> void main() {
>     [5, 6, 7]
>         .map!(a => [idx++, a])
>         .tap!((a) { writeln(a[1..$]); })  /* <-- This can use 
> the
>                                            * lambda syntax as 
> well but
>                                            * note that the 
> return
>                                            * value of the 
> lambda is
>                                            * ignored. So I 
> think this
>                                            * syntax is more
>                                            * helpful. */
>         .walk;
> }
>
> Ali

I don't know, maybe it's something out of science fiction, but 
here's what I want to do :)

struct Tap(alias func, R)
{
     R range;

     alias range this;

     @property auto front()
     {
         immutable string myStr = `func(mixin("range.front"));`;
	immutable string newStr = `mixin(myStr);`;
	writeln(newStr); // I want them to be printed here 
`writeln([5]);`
         mixin(newStr[0 .. $ - 4] ~ `[idx,` ~ newStr[$ - 4 .. $]); 
// I want them to be printed here `[0, 5];`
         return range.front;
     }
}

Is it possible to do using mixins or through any other means? Ie 
I want to catch the moment when `func` is replaced by the 
invocation of `writeln` :)