call Equal method of Expression

问题

when I run this code

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

var method10 = typeof(Expression).GetMethod("Equal", new[] { typeof(Expression), typeof(Expression) });
Expression exp = Expression.Call(method10,left,right);
var lambda = Expression.Lambda<Func<bool>>(exp);
var compiled = lambda.Compile().DynamicInvoke();

I get the below error

Additional information: Expression of type 'System.Int32' cannot be used for parameter of type 'System.Linq.Expressions.Expression' of method 'System.Linq.Expressions.BinaryExpression Equal(System.Linq.Expressions.Expression, System.Linq.Expressions.Expression)'

回答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<Func<bool>>(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<Func<bool>>(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<Func<bool>>(exp);

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

using the Enum.Parse

回答2:

I solved it . thanks guys

Expression left = Expression.Constant(10, typeof(int));
Expression right = Expression.Constant(10, typeof(int));
ExpressionType expressionType;
var tryParseRes = ExpressionType.TryParse("NotEqual", out expressionType);
var exp = Expression.MakeBinary(expressionType, left, right);
var lambda = Expression.Lambda<Func<bool>>(exp);
var compiled = lambda.Compile().DynamicInvoke();
if ((bool)compiled == false)
    areEventCondiotionsPassed = false;

回答3:

Try

var exp = Expression.MakeBinary(ExpressionType.Equal, left, right);

instead of

var method10 = typeof(Expression).GetMethod("Equal", new[] { typeof(Expression), typeof(Expression) });
Expression exp = Expression.Call(method10,left,right);

来源：https://stackoverflow.com/questions/29045951/call-equal-method-of-expression

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lambda

expression