Is there an error in the Go Spec Type Assertions?
A type assertion used in an assignment statement or initialization of the special form
v, ok = x.(T) v, ok := x.(T) var v, ok = x.(T) var v, ok interface{} = x.(T) // dynamic types of v and ok are T and bool
yields an additional untyped boolean value.
What is the last example supposed to be and mean?
var v, ok interface{} = x.(T)
?
I get an error in Go 1.19
syntax error: unexpected interface, expecting := or = or comma
All of those lines are attempting the same operation: a type assertion of x
to type T
. The value, ok
, determines whether or not the assertion was successful. In the last example you provided, the only difference is that instead of Go determining the type for v
and ok
, you've provided a type of interface{}
for both. Declaring v
and ok
as interface{}
doesn't change the values they contain. It would allow you to send them to functions or add them to collections that expect a type of interface{}
, at which point they'd have to be asserted again.