Why Does Method Group Syntax Cause 'Ambiguous Invocation' Errors with Overloaded Delegates (Action vs. Func)?

Method Group Syntax and Ambiguous Invocation with Delegate Overloads

Using method group syntax instead of lambda expressions can lead to ambiguity when dealing with overloaded methods accepting Action or Func<string> delegates. While lambda expressions work seamlessly, method groups trigger an "Ambiguous invocation" error.

The Need for Explicit Casting: Understanding Conversion Rules

The root cause lies in C#'s method group to delegate conversion rules. A method group implicitly converts to a compatible delegate type, meaning parameter types and modifiers must match. Crucially, the return type isn't considered during this implicit conversion.

During overload resolution, the compiler searches for applicable methods. A method is applicable if its parameters can be implicitly converted from the provided arguments. In this scenario, classWithSimpleMethods.GetString() is applicable to both Func<string> and Action because the parameter lists are empty. The compiler cannot choose between these equally valid conversions, hence the ambiguity error. Explicitly casting the method group to either Action or Func<string> resolves this.

C# 7.3 and Beyond: Improved Overload Resolution

As noted by Jon Skeet, C# 7.3 introduced enhancements to overload resolution, mitigating this ambiguity. In many instances, explicit casting is no longer necessary with C# 7.3 and later versions.

The above is the detailed content of Why Does Method Group Syntax Cause 'Ambiguous Invocation' Errors with Overloaded Delegates (Action vs. Func)?. For more information, please follow other related articles on the PHP Chinese website!