In the example above, we defined two data types, Time and Duration. These two data types have different types, but the kind of both of them is int64. So even if we have completely identical data, if their data type has a different name, their Type is different.

The Laws of Reflection in Go

Reflection in the Go language is built around three laws:

1. Through an interface, you can get to a reflection object.

2. Through a reflection object, you can get to an interface.

3. To modify a reflection object, that object must be settable.

Law One: Through an Interface, You Can Get to a Reflection Object

There are two kinds of reflection objects. One is of type Value and the other is of type Type. Through the reflect.ValueOf method, you can access an interface's Value, and similarly, through the reflect.TypeOf method, you can access an interface's Type and Kind.

Law Two: Through a Reflection Object, You Can Get to an Interface

Through a reflect.Value object, you can access the interface. In the example below, we convert a reflect.Value object back to the original data type, which is [ ]int.

So, as in the example above, through the Interface method, you can get to the original interface and then use a type assertion to convert that value to its original value.

Law Three: To Modify a Reflection Object, That Object Must Be Settable

The reflect.Value object has methods whose names start with Set. For example, SetInt is one of them. Depending on the original data type, you can change the data's value using these methods, but before doing so, you need to make sure the reflection object is settable!

The code above will run into an error, because running SetFloat triggers a panic, and the program's execution terminates. This error occurs because our object isn't settable. You can check whether an object is settable with the CanSet method.

Setting (Set) a value on an object that isn't settable causes an error (panic).

To have a settable object, we need to pass a pointer to the ValueOf function (using &), and then, using the Elem method, we can access the value the pointer points to and set it:

We can also use the Set method:

The value we set on the variable must have the same data type; otherwise, the program's execution will run into an error.

One very useful function you can find inside the reflect package is called DeepEqual. This function takes two input parameters, and if the values of these two parameters are equal, it returns true; otherwise, it returns false.

I recommend taking a quick look at the reflect package's list of functions.

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