Package reflect
import "reflect"
type Value
Value is the reflection interface to a Go value.
The zero Value represents no value. Its IsValid method returns false,
its Kind method returns Invalid, its String method returns "", and all other methods panic.
func ValueOf
func ValueOf(i interface{}) Value
ValueOf returns a new Value initialized to the concrete value stored
in the interface i. ValueOf(nil) returns the zero Value.
func (Value) IsValid
func (v Value) IsValid() bool
IsValid reports whether v represents a value. It returns false if v is
the zero Value. If IsValid returns false, all other methods except
String panic. Most functions and methods never return an invalid
value. If one does, its documentation states the conditions
explicitly.
int(0) is a concrete value. ValueOf returns a new Value initialized to the concrete value stored in the interface i. ValueOf(nil) returns the zero Value. IsValid reports whether v represents a concrete value. It returns false if v is the zero Value.
package main
import (
"fmt"
"reflect"
)
func main() {
fmt.Printf("IsValid(nil) %v
", reflect.ValueOf(nil).IsValid())
fmt.Printf("IsValid(int(0)) %v
", reflect.ValueOf(int(0)).IsValid())
}
Output:
IsValid(nil) false
IsValid(int(0)) true
The Go Programming Language Specification
The zero value
When storage is allocated for a variable, either through a declaration
or a call of new, or when a new value is created, either through a
composite literal or a call of make, and no explicit initialization is
provided, the variable or value is given a default value. Each element
of such a variable or value is set to the zero value for its type:
false for booleans, 0 for numeric types, "" for strings, and nil for
pointers, functions, interfaces, slices, channels, and maps.
Package reflect
import "reflect"
func Zero
func Zero(typ Type) Value
Zero returns a Value representing the zero value for the specified
type. The result is different from the zero value of the Value struct,
which represents no value at all. For example, Zero(TypeOf(42))
returns a Value with Kind Int and value 0. The returned value is
neither addressable nor settable.
The Go programming language zero value is not the same as the zero Value in the reflect package. Note the difference in the capitalization of the words Value and value. For example, reflect.Zero returns a Value representing the zero value for the specified type. The result is different from the zero value of the Value struct, which represents no value at all.
