**Does Go\'s Interface Representation Show the Underlying Type or Just the Interface Type?**

In-Depth Analysis of Interface Representation in Go

In the world of Go programming, understanding the intricate details of interface representations is paramount. Two articles have sparked confusion regarding this subject, leaving developers seeking clarity.

Question:

An apparent contradiction arises between two articles discussing interface representation. One article suggests that the type of an interface variable reflects the entire type of the underlying value, while the other claims that it only shows the interface type. This discrepancy creates a dilemma.

Answer:

The seemingly contradictory nature of the articles stems from their focus on different aspects of interface representation. The first article, "Laws of Reflection," explains the representation at the reflection level, while the second article delves into the dynamic dispatch properties of interfaces at runtime.

Reflection-Level Representation:

According to the "Laws of Reflection," an interface variable contains a (value, type) pair. In the example provided, the interface variable r of type io.Reader stores the value tty, which has the underlying type *os.File. This is because the underlying type of the value is still accessible through the interface variable, even though it only exposes the interface methods.

Runtime Representation:

In contrast, the second article examines the dynamic dispatch mechanisms of interfaces at runtime. It explains that at runtime, an interface variable holds a "wrapper object" that provides information about the underlying object's layout. This wrapper object, known as the itable, contains references to the implemented methods.

Reconciling the Two Perspectives:

The apparent contradiction resolves when we recognize that these two perspectives complement each other. At the reflection level, we get an overview of the interface and the underlying value, while at runtime, we delve into the dynamic behavior of the interface.

Key Points:

• Interface variables contain a (value, type) pair at the reflection level.
• At runtime, interfaces use a wrapper object (itable) to facilitate dynamic dispatch.
• The type of an interface variable reflects the static interface type, while the underlying value carries its full type information.

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