call Equal method of Expression

Question

when I run this code

Expression left = Expression.Constant(10, typeof(int));
Expression right = Expression.Constant(10,typeof(int));

var method10 = typeof(Expr         


        

Answer 1

You don't need reflection, unless I'm missing something:

Expression left = Expression.Constant(10, typeof(int));
Expression right = Expression.Constant(10,typeof(int));
Expression exp = Expression.Equal(left, right);
var lambda = Expression.Lambda>(exp);

Clearly you could manually call the int.Equals(int) method...

var method10 = left.Type.GetMethod("Equals", new[] { right.Type });
Expression exp = Expression.Call(left, method10, right);
var lambda = Expression.Lambda>(exp);

but note that there is a subtle difference: Expression.Equal will use the == operator, while the other code will use the Equals method.

If you really want to build an expression from a string:

string methodName = "Equal";
MethodInfo method10 = typeof(Expression).GetMethod(methodName, new[] { typeof(Expression), typeof(Expression) });
Expression exp = (Expression)method10.Invoke(null, new object[] { left, right });
var lambda = Expression.Lambda>(exp);

or

ExpressionType type = (ExpressionType)Enum.Parse(typeof(ExpressionType), methodName);
var exp = Expression.MakeBinary(type, left, right);

using the Enum.Parse