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Fix "TrySingle" signature with honest nullable annotations #801

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Mar 18, 2021
Merged

Fix "TrySingle" signature with honest nullable annotations #801

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16 changes: 6 additions & 10 deletions MoreLinq/Experimental/TrySingle.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -51,7 +51,7 @@ partial class ExperimentalEnumerable
/// than two elements from the sequence.
/// </remarks>

public static (TCardinality Cardinality, T Value)
public static (TCardinality Cardinality, T? Value)
TrySingle<T, TCardinality>(this IEnumerable<T> source,
TCardinality zero, TCardinality one, TCardinality many) =>
TrySingle(source, zero, one, many, ValueTuple.Create);
Expand Down Expand Up @@ -96,19 +96,15 @@ public static (TCardinality Cardinality, T Value)

public static TResult TrySingle<T, TCardinality, TResult>(this IEnumerable<T> source,
TCardinality zero, TCardinality one, TCardinality many,
// TODO review second argument of resultSelector
// ...that can be defaulted to null for nullable references
// so the signature is not quite accurate, but can we do
// something about that?
Func<TCardinality, T, TResult> resultSelector)
Func<TCardinality, T?, TResult> resultSelector)
{
if (source == null) throw new ArgumentNullException(nameof(source));
if (resultSelector == null) throw new ArgumentNullException(nameof(resultSelector));

switch (source.TryGetCollectionCount())
{
case 0:
return resultSelector(zero, default!);
return resultSelector(zero, default);
case 1:
{
var item = source switch
Expand All @@ -120,15 +116,15 @@ public static TResult TrySingle<T, TCardinality, TResult>(this IEnumerable<T> so
return resultSelector(one, item);
}
case {}:
return resultSelector(many, default!);
return resultSelector(many, default);
default:
{
using var e = source.GetEnumerator();
if (!e.MoveNext())
return resultSelector(zero, default!);
return resultSelector(zero, default);
var current = e.Current;
return !e.MoveNext() ? resultSelector(one, current)
: resultSelector(many, default!);
: resultSelector(many, default);
}
}
}
Expand Down