D with experimental features like tuple unpacking

[bearophile]

Denis Shelomovskij:

> D already have undocumented[1] front tuple expansion in foreach 
> over range:
> ---
> import std.algorithm;
> import std.stdio;
>
> void main() {
>     enum s = "this is an example for huffman encoding"d;
>     foreach (c, n; s.dup.sort().release().group())
>         writefln("'%s'  %s", c, n);
> }


I know, but it doesn't work in the case of my code I have shown, 
with a SortedRange of 2-tuples:

void main() {
     auto s = "this is an example for huffman encoding"d;
     foreach (c, n; s.dup.sort().release.group.encode)
         writefln("'%s'  %s", c, n);
}

---------------------------

Jacob Carlborg:

>> auto (lof, loa) = heap.front;
>
> How is front suddenly returning two elements?

It is not returning two elements. In D you can't return two 
elements. It is returning a 2-Tuple. You see the 2-tuples are 
built by the map() and then used to create a heap:

auto heap = sf.map!(((c, f)) => tuple(f, 
...)).array.heapify!q{...};


And this proposed syntax performs pattern matching on that 
2-tuple, unpacking it into two variables (Hara has implemented 
this already):

auto (lof, loa) = ...;

In Haskell, Scala, Python, F#, etc, the semantics and syntax are 
similar.

Bye,
bearophile