What Do Parentheses Before a Go Function Name Mean?

Understanding the Meaning of Function Declarations with Parentheses Before Function Name

When encountering function declarations in Go with parentheses containing expressions before the function name, it becomes necessary to clarify their meaning and the role they play in the function declaration.

Receiver Expressions

The expressions enclosed within parentheses, as in (h handler) and (s *GracefulServer), are known as "receiver expressions." They specify the type of the receiver, which is the entity on which the function operates.

Receiver Types

In the example, (h handler) represents a value receiver of type handler, while (s *GracefulServer) represents a pointer receiver of type GracefulServer. The difference between value and pointer receivers lies in how they access the receiver's data.

Function Meaning

With the understanding of receiver expressions, we can now interpret the entire function declarations:

• func (h handler) ServeHTTP(w http.ResponseWriter, r http.Request) {...}: This function is a method associated with the handler type. It takes two parameters, w of type http.ResponseWriter and r of type http.Request, and performs operations on the handler type.
• func (s GracefulServer) BlockingClose() bool {...}: This function is also a method, associated with the GracefulServer type. It does not take any parameters and returns a boolean value. It operates on the *GracefulServer type.

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