[Issue 9612] std.range.Cycle.opSlice tests on the bounds are missing

[d-bugmail at puremagic.com]

http://d.puremagic.com/issues/show_bug.cgi?id=9612


bearophile_hugs at eml.cc changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |accepts-invalid
                 CC|                            |bearophile_hugs at eml.cc
            Summary|cycle() and opSlice         |std.range.Cycle.opSlice
                   |                            |tests on the bounds are
                   |                            |missing


--- Comment #1 from bearophile_hugs at eml.cc 2013-02-27 15:26:58 PST ---
I was about to file this bug myself, this is the text I was going to use:

This code:

void main() {
    auto a = [0,1,2,3,4,5,6,7,8,9][5 .. 2];
}


Gives the correct compile-time error:

temp3.d(2): Error: array slice [5 .. 2] is out of bounds
temp3.d(2): Error: array slice [5 .. 2] is out of bounds



While this gives no compile-time nor run-time errors:

import std.stdio: writeln;
import std.range: iota, cycle, take;
void main() {
    iota(10).cycle()[5 .. 2].take(4).writeln();
}

And prints (DMD 2.063alpha):

[5, 6, 7, 8]


The opSlice of cycle() lacks pre-conditions or tests, and there are not enough
unittests to catch this bug:

        auto opSlice(size_t i, size_t j)
        {
            auto retval = this.save;
            retval._index += i;
            return takeExactly(retval, j - i);
        }


j - i is positive because those numbers are unsigned, and because D lacks
run-time errors for integral overflows:


import std.stdio;
struct Foo {
    auto opSlice(size_t i, size_t j) {
        writeln(j - i);
    }
}
void main() {
    Foo f;
    f[5 .. 2];
}


Output:
4294967293


Maybe there is a need to run something similar to QuickCheck on Phobos:
http://en.wikipedia.org/wiki/QuickCheck

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