public static bool IsNull(ExpressionNode expression)
{
ConstantExpression constantExpression = expression as ConstantExpression;
return(constantExpression != null && constantExpression.IsNullValue);
}
public override ExpressionNode VisitMethodInvocationExpression(MethodInvocationExpression expression)
{
base.VisitMethodInvocationExpression(expression);
// Constant folding must not be applied if the method is non-deterministic.
if (!expression.Method.IsDeterministic)
return expression;
// Check if target is a constant or even null.
ConstantExpression targetAsConstant = expression.Target as ConstantExpression;
if (targetAsConstant == null)
return expression;
if (targetAsConstant.IsNullValue)
return LiteralExpression.FromTypedNull(expression.ExpressionType);
// Check if all arguments are constants or at least one argument
// is null.
ConstantExpression[] constantArguments = new ConstantExpression[expression.Arguments.Length];
bool allArgumentsAreConstants = true;
for (int i = 0; i < constantArguments.Length; i++)
{
constantArguments[i] = expression.Arguments[i] as ConstantExpression;
if (constantArguments[i] == null)
{
// Ok, one argument is not a constant
// But don't stop: If an argument is null we can still calculate the result!
allArgumentsAreConstants = false;
}
else if (constantArguments[i].IsNullValue)
{
// We found a null. That means the invocation will also yield null.
return LiteralExpression.FromTypedNull(expression.ExpressionType);
}
}
if (allArgumentsAreConstants)
{
try
{
return LiteralExpression.FromTypedValue(expression.GetValue(), expression.ExpressionType);
}
catch (RuntimeException ex)
{
_errorReporter.CannotFoldConstants(ex);
}
}
return expression;
}