private Type ResolveExpressionCommonType(Type left, Type right, bool allowStringConcat, bool allowBothImplicit, bool allowObjectCoercion)
{
Require.NotNull(left, "left");
Require.NotNull(right, "right");
// No casting required.
if (left == right)
{
return(left);
}
if (allowObjectCoercion)
{
if (left == typeof(object))
{
return(right);
}
if (right == typeof(object))
{
return(left);
}
}
// Special cast for adding strings.
if (allowStringConcat && (left == typeof(string) || right == typeof(string)))
{
return(typeof(string));
}
// Can we cast implicitly?
var leftTable = TypeUtil.GetImplicitCastingTable(left);
var rightTable = TypeUtil.GetImplicitCastingTable(right);
if (leftTable != null && rightTable != null)
{
// See whether one of the types appears in the other.
foreach (var leftType in leftTable)
{
if (leftType == right)
{
return(leftType);
}
}
foreach (var rightType in rightTable)
{
if (rightType == left)
{
return(rightType);
}
}
// Otherwise, find the first common type.
int lowest = int.MaxValue;
for (int i = 0; i < leftTable.Count; i++)
{
for (int j = 0; j < rightTable.Count; j++)
{
if (leftTable[i] == rightTable[j])
{
lowest = Math.Min(lowest, j);
}
}
}
if (lowest != int.MaxValue)
{
if (
allowBothImplicit ||
(IsAllowableImplicit(left, rightTable[lowest]) && IsAllowableImplicit(right, rightTable[lowest]))
)
{
return(rightTable[lowest]);
}
}
}
// We can't cast implicitly.
throw new ExpressionsException("Cannot resolve expression type", ExpressionsExceptionType.TypeMismatch);
}
