How Do I Get the reflect.Type of an Uninitialized Interface in Go?

Determining the reflect.Type of an Interface

To ascertain whether a type implements an interface using the reflect package, it is necessary to provide a reflect.Type to reflect.Type.Implements(). However, obtaining this type can sometimes seem enigmatic, especially for uninitialized interfaces such as error.

Uninitialized Error Interface

Attempting to determine the type of an uninitialized error (interface) using reflect.TypeOf(err).Kind() will result in a panic when Kind() is invoked.

Solution

To correctly obtain the type of an interface like error, it is necessary to first create a pointer to the interface and then use Elem() on the resulting type. This can be accomplished in two ways:

Verbose Method:

var err error
t := reflect.TypeOf(&err).Elem()

One-Line Method:

t := reflect.TypeOf((*error)(nil)).Elem()

By following these approaches, you can effectively retrieve the reflect.Type of an interface, regardless of its initialization state.

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