Why Can't I Assign an Anonymous Method to a `var` Variable in C#?

Why Anonymous Method Cannot Assign to Var

When encountering an anonymous method like:

delegate(string value) {
    return value != "0";
}

The compiler is faced with a challenge. Unlike a typed lambda expression such as:

Func comparer = delegate(string value) {
    return value != "0";
};

The anonymous method doesn't explicitly specify a delegate type. The compiler must infer that type based on the method's signature. However, there are infinite potential delegate types that satisfy these conditions, with varying parameters and return values.

Inferring the type for an anonymous method presents several issues:

• Lack of Consistency: Assigning a lambda expression to var implies inference to the Func type. However, with anonymous methods, there is no such precedence, leading to inconsistencies in handling multiple arguments cases.
• Ambiguity: In cases like var x2 = y => 123, the compiler cannot determine the parameter type.
• Undefined Return Type: Some anonymous methods have unspecified return types, which could be any reference or nullable value type.
• Indeterminable Function Scope: Statement lambdas and functions cannot be distinguished in cases like var x5 = (int y) => q = y.
• Special Syntax and Limitation: Using anonymous methods requires the delegate keyword, adding unnecessary syntax compared to lambda expressions. The delegate form also lacks features like expression trees and message passing.

Therefore, the compiler error "Cannot assign anonymous method to an implicitly-typed local variable" prevents the use of var with anonymous methods.

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