问题
I'm using NCalc to evaluate complex expressions. But I've found a major problem.
A simple formula like new Expression("Abs(-1) + Cos(2)").Evaluate() throws the exception
Operator '+' can't be applied to operands of types 'decimal' and 'double
In C# code Math.Abs(-1) + Math.Cos(2) works, so either I'm doing something wrong or there is a bug in NCalc.
Does anyone have the same problem?
Does anyone have a solution?
The only thread i found on the project's website related to this error is quite old and talks about editing the source code. https://ncalc.codeplex.com/discussions/346702
I also posted a question on their forum but StackOverflow is usualy more dynamic. https://ncalc.codeplex.com/discussions/613634
回答1:
Ok. I looked at the source code. And here is what I found.
The Abs(-1) part of the expression is always evaluated as a decimal
Result = Math.Abs(Convert.ToDecimal(
Evaluate(function.Expressions[0]))
);
Cos(2) is evaluated as double
Result = Math.Cos(Convert.ToDouble(Evaluate(function.Expressions[0])));
And C# does not allow you to add these two types together.
The reason that Math.Abs(-1) + Math.Cos(2) works is that Math.Abs(-1) actually evaluates as int. And you can perfectly add an int to double.
You can not compile this piece for example (note m for decimal). Math.Abs(-1m) + Math.Cos(2);
which is actually what NCalc is trying to do when you type out
new Expression("Abs(-1) + Cos(2)").Evaluate()
I would call this a bug. You can try to edit the source and try to fix this problem or find some other option.
回答2:
After a brief chat with btevfik (helpfull fella) we have come to the conclusion that this is a bug in NCalc. I guess I'll have to analyse the source and fix it.
I still accept answers though...
来源：https://stackoverflow.com/questions/29255487/operator-cant-be-applied-to-operands-of-types-decimal-and-double-ncal