protected override BoundExpression RewriteCaseExpression(BoundCaseExpression node)
{
var whenPassthru = CurrentPassthru;
var labels = node.CaseLabels;
foreach (var oldLabel in labels)
{
_passthruStack.Push(whenPassthru);
var when = RewriteExpression(oldLabel.Condition);
_passthruStack.Pop();
var thenPassthru = Expression.Or(whenPassthru, Expression.Not(when));
_passthruStack.Push(thenPassthru);
var then = RewriteExpression(oldLabel.ThenExpression);
_passthruStack.Pop();
var label = oldLabel.Update(when, then);
labels = labels.Replace(oldLabel, label);
whenPassthru = Expression.Or(whenPassthru, when);
}
_passthruStack.Push(whenPassthru);
var elseExpression = RewriteExpression(node.ElseExpression);
_passthruStack.Pop();
return(node.Update(labels, elseExpression));
}
private Expression BuildCaseLabel(BoundCaseExpression caseExpression, int caseLabelIndex)
{
if (caseLabelIndex == caseExpression.CaseLabels.Length)
{
return(caseExpression.ElseExpression == null
? BuildNullValue(caseExpression.Type)
: BuildLiftedExpression(caseExpression.ElseExpression));
}
var caseLabel = caseExpression.CaseLabels[caseLabelIndex];
var condition = caseLabel.Condition;
var result = caseLabel.ThenExpression;
return
(Expression.Condition(
Expression.Equal(
BuildLiftedExpression(condition),
BuildNullableTrue()
),
BuildLiftedExpression(result),
BuildCaseLabel(caseExpression, caseLabelIndex + 1)
));
}
private Expression BuildCaseExpression(BoundCaseExpression expression)
{
return(BuildCaseLabel(expression, 0));
}
