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min must be stable #7605

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Aug 28, 2020
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min must be stable #7605

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17 changes: 15 additions & 2 deletions std/algorithm/comparison.d
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Original file line number Diff line number Diff line change
Expand Up @@ -1713,8 +1713,8 @@ if (T.length >= 2)

//Do the "min" proper with a and b
import std.functional : lessThan;
immutable chooseA = lessThan!(T0, T1)(a, b);
return cast(typeof(return)) (chooseA ? a : b);
immutable chooseB = lessThan!(T1, T0)(b, a);
return cast(typeof(return)) (chooseB ? b : a);
}

///
Expand Down Expand Up @@ -1757,6 +1757,19 @@ store the lowest values.
assert(min(Date.max, Date.min) == Date.min);
}

// min must be stable: when in doubt, return the first argument.
@safe unittest
{
assert(min(1.0, double.nan) == 1.0);
assert(min(double.nan, 1.0) is double.nan);
static struct A {
int x;
string y;
int opCmp(const A a) const { return int(x > a.x) - int(x < a.x); }
}
assert(min(A(1, "first"), A(1, "second")) == A(1, "first"));
}

// mismatch
/**
Sequentially compares elements in `r1` and `r2` in lockstep, and
Expand Down