Convert Method Group to Expression

问题:

I'm trying to figure out of if there is a simple syntax for converting a Method Group to an expression. It seems easy enough with lambdas, but it doesn't translate to methods:

Given

public delegate int FuncIntInt(int x);

all of the below are valid:

Func<int, int> func1 = x => x;
FuncIntInt del1 = x => x;
Expression<Func<int, int>> funcExpr1 = x => x;
Expression<FuncIntInt> delExpr1 = x => x;

But if i try the same with an instance method, it breaks down at the Expressions:

Foo foo = new Foo();
Func<int, int> func2 = foo.AFuncIntInt;
FuncIntInt del2 = foo.AFuncIntInt;
Expression<Func<int, int>> funcExpr2 = foo.AFuncIntInt; // does not compile
Expression<FuncIntInt> delExpr2 = foo.AFuncIntInt;      //does not compile

Both of the last two fail to compile with "Cannot convert method group 'AFuncIntInt' to non-delegate type 'System.Linq.Expressions.Expression<...>'. Did you intend to invoke the method?"

So is there a good syntax for capturing a method grou in an expression?

thanks, arne

回答1:

How about this?

  Expression<Func<int, int>> funcExpr2 = (pArg) => foo.AFuncIntInt(pArg);
  Expression<FuncIntInt> delExpr2 = (pArg) => foo.AFuncIntInt(pArg);

回答2:

It is also possible to do it using NJection.LambdaConverter a Delegate to LambdaExpression converter Library

public class Program
{
    private static void Main(string[] args) {
       var lambda = Lambda.TransformMethodTo<Func<string, int>>()
                          .From(() => Parse)
                          .ToLambda();            
    }   

    public static int Parse(string value) {
       return int.Parse(value)
    } 
}