/// <summary>
/// Returns a new Query where each new element in the sequence is an instance of the PrevPair struct.
/// The value field of the pair will point to an element in the current sequence, and the prev field will
/// point to an element that comes 'offset' elements before the current element. If 'includeStart' is true,
/// the sequence will also include elements that have no previous element.
///
/// For example, with an offset of 2 and with includeStart as true, the sequence:
/// A, B, C, D, E, F
/// is transformed into:
/// (A,_) (B,_) (C,A) (D,B) (E,C) (F,D)
/// </summary>
public static Query <PrevPair <T> > WithPrevious <T>(this Query <T> query,
int offset = 1, bool includeStart = false)
{
using (var slice = query.Deconstruct()) {
int resultCount = includeStart ? slice.Count : Mathf.Max(0, slice.Count - offset);
var dstArray = ArrayPool <PrevPair <T> > .Spawn(resultCount);
int dstIndex = 0;
if (includeStart)
{
for (int i = 0; i < Mathf.Min(slice.Count, offset); i++)
{
dstArray[dstIndex++] = new PrevPair <T>()
{
value = slice[i],
prev = default(T),
hasPrev = false
};
}
}
for (int i = offset; i < slice.Count; i++)
{
dstArray[dstIndex++] = new PrevPair <T>()
{
value = slice[i],
prev = slice[i - offset],
hasPrev = true
};
}
return(new Query <PrevPair <T> >(dstArray, resultCount));
}
}
public bool TryGetNext(out PrevPair <SourceType> t)
{
top:
SourceType value;
if (_mainOp.TryGetNext(out value))
{
if (_offsetLeft > 0)
{
_offsetLeft--;
if (!_includeStart)
{
goto top;
}
t = new PrevPair <SourceType>()
{
value = value,
prev = default(SourceType),
hasPrev = false
};
}
else
{
SourceType prev;
_delayedOp.TryGetNext(out prev);
t = new PrevPair <SourceType>()
{
value = value,
prev = prev,
hasPrev = true
};
}
return(true);
}
else
{
t = default(PrevPair <SourceType>);
return(false);
}
}
