How to check if the value of a parameterize type is the zero value?-CodePudding

The generics proposal has a section on how to return the zero value of a parameterized type, but it does not mention how to check if a value of a parameterized type is the zero value. The only way I can think of is to use reflect.ValueOf(...).IsZero(), is there an alternative?

CodePudding user response：

If the type is comparable, then compare the value to a variable set to the zero value of the type.

  var zero T
  isZero := v == zero

Use the reflect package if the type is not comparable:

  isZero := reflect.ValueOf(&v).Elem().IsZero()

CodePudding user response：

Use the equal operator with the *new(T) idiom. The constraint of the generic param must be, or embed,comparable to support the equality operator, or specify a type set of comparable types:

func IsZero[T comparable](v T) bool {
    return v == *new(T)
}

If you can’t constrain T to comparable then you’re left with reflection. Zombo’s suggestion to address the variable like this:

is superior to simply reflect.ValueOf(v).IsZero() because ValueOf takes an interface{} argument and if v just happens to be an interface{} you would loose that information. I don’t think that with generics you will often instantiate a function with interface{} but it’s worth knowing.