How Can We Efficiently Compare the Equality of Lambda Expressions in C#?

Comparing the Equality of Lambda Expressions Efficiently

Challenge:
Given a method signature:

public bool AreTheSame<T>(Expression<Func<T, object>> exp1, Expression<Func<T, object>> exp2) 

Determine the most effective method to ascertain if the two expressions are equivalent. This evaluation should only support straightforward MemberExpressions, like c => c.ID.

Proposed Solution:
An optimized version of Marc's code that supports arrays, new operators, and more is presented below. It employs a more elegant method of comparing ASTs.

public static class LambdaCompare
{
    public static bool Eq<TSource, TValue>(
        Expression<Func<TSource, TValue>> x,
        Expression<Func<TSource, TValue>> y)
    {
        return ExpressionsEqual(x, y, null, null);
    }

    ...

    private static bool ExpressionsEqual(Expression x, Expression y, LambdaExpression rootX, LambdaExpression rootY)
    {
        ...
    }

    ...
}

Detailed Explanation:

• This code checks if the two expressions are the same by reference before comparing them value-by-value.
• It evaluates whether they are both constant expressions and, if so, determines their values.
• If the expressions are not the same type, the function returns false.
• For lambda expressions, it compares the parameters and body of the expressions.
• For member expressions, it compares the member and the underlying expression.
• For binary expressions, it compares the method, left expression, and right expression.
• For unary expressions, it compares the method and operand.
• For parameter expressions, it compares their indices in the parameter lists.
• For method call expressions, it compares the method, object, and arguments.
• For member init expressions, it compares the new expression and member bindings.
• For new array expressions, it compares the elements.
• For new expressions, it compares the constructor, arguments, and members.
• For conditional expressions, it compares the test, if false, and if true expressions.
• If none of the above criteria match, the function throws a NotImplementedException.

Advantages:

• Supports a wide range of expression types.
• Compares ASTs in a more efficient and elegant manner.
• Available as a NuGet package for easy integration.

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