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c#validationlambdaguard-clause

Guard checking of lambdas

I usually perform guard checking like so:

public void doStuff(Foo bar, Expression<Func<int, string>> pred) {
  if (bar == null) throw new ArgumentNullException();
  if (pred == null) throw new ArgumentNullException();
  // etc...
}

I've seen this extra check which ensures that the predicate is actually a lambda:

  if (pred.NodeType != ExpressionType.Lambda) throw new ArgumentException();

The ExpressionType enum has many possibilities, but I don't understand how any of them would apply because I assumed the compiler would only allow a lambda.

Q1: Is there benefit to this? We do thorough guard checking of all inputs, so does this add value?

Q2: Is there a performance penalty - i.e. does it take longer than a regular type/bounds/null check?

Solution

  • Func<int, string> is a delegate that could be the address of a function or inline as lambda expression [ () => x ] .

    Expression<TDelegate> inherits from LambdaExpression and the NodeType of an Expression<TDelegate> is always ExpressionType.Lambda.

    So, I think that kind of defensive code is not needed.