Bug 19644 – std.range.takeOne opSlice asserts incorrectly when operating on non-forward input range

std.range.takeOne supports slicing. The valid slice is [0..1]. However, the implementation for non-forward input ranges incorrectly asserts on this call. This is due incorrectly checking for the second argument being less-than length. The test should be less-than-equal. A PR is in progress. --- Test program (test.d) --- import std.range; import std.stdio; struct ValInputRange(R) { R data; this(R _data) pure @safe nothrow { data = _data; } @property bool empty() pure @safe nothrow { return data.empty; } @property auto front() pure @safe nothrow { assert(!empty); return data.front; } void popFront() pure @safe nothrow { assert(!empty); data.popFront(); } } auto valInputRange(R)(R range) { return ValInputRange!R(range); } void main(string[] args) { auto a = [1, 2, 3, 4, 5]; auto r1 = a.takeOne; auto q1 = r1[0..1]; // Works fine. writeln(q1); auto r2 = a.valInputRange.takeOne; auto q2 = r2[0..1]; // Asserts here. writeln(q2); } ---------------------------- Run: $ dmd --version DMD64 D Compiler v2.084.0 $ dmd test.d $ ./test [1] core.exception.AssertError@/INSTALLDIR/osx/bin/../../src/phobos/std/range/package.d(2658): Attempting to index a takeOne out of bounds ---------------- ??:? _d_assert_msg [0x2db17d8] ??:? pure nothrow @nogc @safe std.range.takeOne!(test.ValInputRange!(int[]).ValInputRange).takeOne(test.ValInputRange!(int[]).ValInputRange).Result std.range.takeOne!(test.ValInputRange!(int[]).ValInputRange).takeOne(test.ValInputRange!(int[]).ValInputRange).Result.opSlice(ulong, ulong) [0x2da45f8] ??:? _Dmain [0x2d9867b]

PR 6853: https://github.com/dlang/phobos/pull/6853

Merged: https://github.com/dlang/phobos/commit/9f545db8605cc7d5788e8c6ec1992f6414c8ea16