From b89a54e5c68df4d4d9b39512accd3a69b082cbba Mon Sep 17 00:00:00 2001
From: Russ Cox
-asserts that the value stored in x is of type T.
+asserts that x is not the zero interface value
+and that the value stored in x is of type T.
The notation x.(T) is called a type assertion.
The type of x must be an interface type.
x is identical to the type T
(§Type identity and compatibility).
If T is an interface type, x.(T) asserts that the dynamic type
of T implements the interface T (§Interface types).
-TODO: gri wants an error if x is already of type T.
If the type assertion holds, the value of the expression is the value -- 2.52.0