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digitalmars.D.bugs - [Issue 11820] New: std.algorithm.remove does not function with `alias this`

reply d-bugmail puremagic.com writes:
https://d.puremagic.com/issues/show_bug.cgi?id=11820

           Summary: std.algorithm.remove does not function with `alias
                    this`
           Product: D
           Version: D2
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: major
          Priority: P2
         Component: Phobos
        AssignedTo: nobody puremagic.com
        ReportedBy: msoucy csh.rit.edu



Created an attachment (id=1306)
Sample file from dpaste

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`.

Issue was traced to this commit:
https://github.com/D-Programming-Language/phobos/pull/1162/files

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Dec 25 2013
next sibling parent d-bugmail puremagic.com writes:
https://d.puremagic.com/issues/show_bug.cgi?id=11820




It seems that this affects more than just std.algorithm.remove - reverse also
causes compile errors, possibly others.

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Dec 27 2013
prev sibling next sibling parent d-bugmail puremagic.com writes:
https://d.puremagic.com/issues/show_bug.cgi?id=11820


Matt Soucy <msoucy csh.rit.edu> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Severity|major                       |regression


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Jan 01 2014
prev sibling parent d-bugmail puremagic.com writes:
https://d.puremagic.com/issues/show_bug.cgi?id=11820


monarchdodra gmail.com changed:

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




 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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Jan 02 2014