There are many cases using nil in golang. For example:
func (u *URL) Parse(ref string) (*URL, error) {
refurl, err := Parse(ref)
if err != nil {
return nil, err
}
return u.ResolveReference(refurl), nil
}
but we can't use it like this:
var str string //or var str int
str = nil
the golang compiler will throw a can't use nil as type string in assignment
error.
Looks like nil
can only be used for a pointer of struct and interface. If that is the case, then what does it mean?
and when we use it to compare to the other object, how do they compare, in other words, how does golang determine one object is nil?
EDIT:For example, if an interface is nil, its type and value must be nil at the same time. How does golang do this?
nil s in Go. nil is a frequently used and important predeclared identifier in Go. It is the literal representation of zero values of many kinds of types. Many new Go programmers with experiences of some other popular languages may view nil as the counterpart of null (or NULL ) in other languages.
Nil is a type with a single value, nil, whose main property is to be different from any other value. As we have seen, a global variable has a nil value by default, before a first assignment, and you can assign nil to a global variable to delete it.
In Golang, when a variable is declared without an initialization value, its value will be set to the type's zero value. The zero value of a Slice is nil, so in our example above, when we declare var foo []string the value of foo is actually nil not an empty slice of string [] .
The last example shows that nil is not a type therefore it cannot be used to be assigned to a value without a type. What happened here? We can clearly see (and based on previous rules) that both p and i has value nil but the condition is evaluated into false. This is not a bug it is a legitimate Golang behaviour.
In Go, nil
is the zero value for pointers, interfaces, maps, slices, channels and function types, representing an uninitialized value.
nil
doesn't mean some "undefined" state, it's a proper value in itself. An object in Go is nil
simply if and only if it's value is nil
, which it can only be if it's of one of the aforementioned types.
An error
is an interface, so nil
is a valid value for one, unlike for a string
. For obvious reasons a nil
error represents no error.
nil
in Go is simply the NULL
pointer value of other languages.
You can effectively use it in place of any pointer or interface (interfaces are somewhat pointers).
You can use it as an error, because the error type is an interface.
You can't use it as a string because in Go, a string is a value.
nil
is untyped in Go, meaning you can't do that:
var n = nil
Because here you lack a type for n
. However, you can do
var n *Foo = nil
Note that nil
being the zero value of pointers and interfaces, uninitialized pointers and interfaces will be nil
.
nil is also a value but only difference is- it is empty.
In Javascript for the un-initialized variable will be undefined. In the same way Golang has nil as default value for all the un-initalized data types.
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