[Issue 11820] std.algorithm functions do not function properly with `alias this`

[d-bugmail at puremagic.com]

https://d.puremagic.com/issues/show_bug.cgi?id=11820


monarchdodra at gmail.com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
                 CC|                            |monarchdodra at gmail.com
         Resolution|                            |INVALID


--- Comment #2 from monarchdodra at gmail.com 2014-01-02 05:26:12 PST ---
> In situations such as the attached, std.algorithm.remove produces a
compile-time error when used on an object that fulfills its requirements only
because of `alias this`.

Technically, "remove" does not produce a compile time error, because the object
does *not* fulfill the requirements, and the compiler finds no adequate match.

remove (and reverse) require input to be at *least* a forward range. Foo is
*not* a forward range because the type returned by `foo.save` is not `Foo`,
it's an int[].

This violates the requirement that you can do this with a forward range:
Foo f;
f = f.save; //Fails

--------
The two workarounds are:
1) Pass an explicit f.bar
2) Improve Foo to be an actual forward range: give it its own "save" primitive,
as well as the slicing primitives (for hasSlicing).

Also, don't forget to *re*-assign the result of "remove" after calling it, or
you'll just observe "shuffled" elements.

//----
import std.stdio;
import std.algorithm;
import std.range;

struct Foo {
    int[] bar;
    alias bar this;
    inout(Foo) save() @property inout
    {
        return this;
    }
    inout(Foo) opSlice(size_t i, size_t j) @property inout
    {
        return inout(Foo)(bar[i .. j]);
    }
}

void main()
{
    Foo f;
    static assert(isRandomAccessRange!Foo);
    static assert(hasSlicing!Foo);
    f = [1,3,5,7,9];
    (f = remove(f, 0)).writeln();
    (f.bar = remove(f.bar, 0)).writeln();
    (f = remove(f, 0)).writeln();
    (f.bar = remove(f.bar, 0)).writeln();
}
//----

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