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Checking for Nil and Nil Interfaces in Go
When working with interfaces in Go, it's often necessary to check whether an interface is nil or contains a nil value. However, the standard approach using reflection can be verbose and error-prone.
For example, consider the following helper function:
func isNil(a interface{}) bool { defer func() { recover() }() return a == nil || reflect.ValueOf(a).IsNil() }
This function uses reflection to check if the value is nil, but it requires a deferred recover() to handle panics when the value's type is not supported.
A More Direct Approach
As the answer to the original question suggests, a simpler and more reliable approach is to use direct comparison for nil interfaces and always allow assignment of nil to untyped interfaces. Here's how:
func isNil(a interface{}) bool { return a == nil }
This function will correctly check for both nil interfaces and nil values within interfaces.
When Assignment of (*T)(nil) Is Allowed
The approach outlined above assumes that you will never assign (*T)(nil) to an interface. If this is not the case, you may need to use reflection to check for nil values:
func isNil(a interface{}) bool { if a == nil { return true } v := reflect.ValueOf(a) if v.Kind() == reflect.Ptr && v.IsNil() { return true } return false }
However, it's generally recommended to avoid assigning (*T)(nil) to interfaces, as it can lead to subtle bugs. By enforcing the rule of never storing (*T)(nil) in interfaces, you can simplify your code and increase its reliability.
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