Is there a generic constraint I could use for the + operator?

问题

is there some \'where\' type contraints in can add to make the follwing code compile ?

public class Plus<T> : BinaryOperator<T> where T : ...
{
    public override T Evaluate(IContext<T> context)
    {
        return left.Evaluate(context) + right.Evaluate(context);
    }
}

Thanks :)

回答1:

There are no such devices in C#. A few options are available, though:

in C# 4.0 and .NET 4.0 (or above), use dynamic, which supports + but offers no compile time checking
in .NET 3.5 (or above), MiscUtil offers an Operator class which makes operators available as methods - again, without any compile-time checking

So either:

return (dynamic)left.Evaluate(context) + (dynamic)right.Evaluate(context);

return Operator.Add(left.Evaluate(context), right.Evaluate(context));

回答2:

The Type parameter constraints in C# are very limited and is listed here. So the answer is no as far as compile time check goes. If T is a type that you create and manage, one way to go about it would be to

interface IAddable 
{
   IAddable Add(IAddable foo);
}

and implement IFoo for all your types and use where T: IAddable as constraint and use Add() instead of +

回答3:

Using a generic constraints you can force T

to be a reference type or a value type
to inherit from a certain class
to implement certain interface
to have parameterless constructor

But that's all. You can't force the existence of the static operator+ on it.

来源：https://stackoverflow.com/questions/5997107/is-there-a-generic-constraint-i-could-use-for-the-operator

标签

generics

constraints