Caller info attributes ^{C# 5.0} have been useful for capturing the calling member name, file path and line number.

C# 10.0 provides a CallerArgumentExpression attribute that can be applied to a method parameter in order to capture the source code passed to another parameter.

Code

Now

ArgumentNullException.ThrowIfNull(customerId);

var customer = Find(c => c.Id == customerId);
// ...
Customer Find(Func<Customer, bool> predicate, [CallerArgumentExpression("predicate")] string code = "")
{
    return db.Customers.FirstOrDefault(predicate)
        ?? throw new EntityNotFoundException("Could not find Customer matching " + code);
}

Before

if (customerId == null) throw new ArgumentNullException(nameof(customerId));

var customer = Find(c => c.Id == customerId, "c => c.Id == customerId");
// ...
Customer Find(Func<Customer, bool> predicate, string code = "")
{
    return db.Customers.FirstOrDefault(predicate)
        ?? throw new EntityNotFoundException("Could not find Customer matching " + code);
}

Notes

• The parameter receiving the expression must be optional; the compiler fills it in only when the caller omits it
• ArgumentNullException.ThrowIfNull, added in .NET 6, uses this attribute to report the argument's name
• Reduces the need to repeat nameof ^{C# 6.0} in guard clauses

More information

• Specification
• C# Reference