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Remove enumerator allocation in for (HashSet, HashSet) comparisons in SetEquals and IsProperSupersetOf. #78613

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Merged
eiriktsarpalis merged 2 commits into from
Nov 21, 2022
Merged

Remove enumerator allocation in for (HashSet, HashSet) comparisons in SetEquals and IsProperSupersetOf. #78613

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c914d45
Remove enumerator allocation in for (HashSet, HashSet) comparisons in
madelson Nov 20, 2022
c99b80f
Address feedback from PR.
madelson Nov 21, 2022
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36 changes: 13 additions & 23 deletions src/libraries/System.Private.CoreLib/src/System/Collections/Generic/HashSet.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -706,7 +706,15 @@ public bool IsSupersetOf(IEnumerable<T> other)
}
}

return ContainsAllElements(other);
foreach (T element in other)
{
if (!Contains(element))
{
return false;
}
}

return true;
}

/// <summary>Determines whether a <see cref="HashSet{T}"/> object is a proper superset of the specified collection.</summary>
Expand Down Expand Up @@ -743,7 +751,7 @@ public bool IsProperSupersetOf(IEnumerable<T> other)
}

// Now perform element check.
return ContainsAllElements(otherAsSet);
return otherAsSet.IsSubsetOfHashSetWithSameComparer(this);
}
}

Expand Down Expand Up @@ -811,8 +819,8 @@ public bool SetEquals(IEnumerable<T> other)
}

// Already confirmed that the sets have the same number of distinct elements, so if
// one is a superset of the other then they must be equal.
return ContainsAllElements(otherAsSet);
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@madelson madelson Nov 20, 2022

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After these changes, there is now only one caller for ContainsAllElements(IEnumerable<T>) (IsSupersetOf). Should the helper method just be inlined there?

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@stephentoub stephentoub Nov 20, 2022

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Sure

// one is a subset of the other then they must be equal.
return IsSubsetOfHashSetWithSameComparer(otherAsSet);
}
else
{
Expand Down Expand Up @@ -1178,24 +1186,6 @@ private bool AddIfNotPresent(T value, out int location)
return true;
}

/// <summary>
/// Checks if this contains of other's elements. Iterates over other's elements and
/// returns false as soon as it finds an element in other that's not in this.
/// Used by SupersetOf, ProperSupersetOf, and SetEquals.
/// </summary>
private bool ContainsAllElements(IEnumerable<T> other)
{
foreach (T element in other)
{
if (!Contains(element))
{
return false;
}
}

return true;
}

/// <summary>
/// Implementation Notes:
/// If other is a hashset and is using same equality comparer, then checking subset is
Expand Down Expand Up @@ -1391,7 +1381,7 @@ private unsafe void SymmetricExceptWithEnumerable(IEnumerable<T> other)
/// <param name="other"></param>
/// <param name="returnIfUnfound">Allows us to finish faster for equals and proper superset
/// because unfoundCount must be 0.</param>
private unsafe (int UniqueCount, int UnfoundCount) CheckUniqueAndUnfoundElements(IEnumerable<T> other, bool returnIfUnfound)
private (int UniqueCount, int UnfoundCount) CheckUniqueAndUnfoundElements(IEnumerable<T> other, bool returnIfUnfound)
{
// Need special case in case this has no elements.
if (_count == 0)
Expand Down