Answer

The blank identifier (_) is a special identifier in Go that serves to ignore values. It is used when the return value of a function is not needed, when importing packages solely for the purpose of calling their init, or when implementing interfaces.

Examples:

// Ignoring the returned error value
data, _ := ioutil.ReadFile("file.txt")

// Importing a package solely for side effects
import _ "net/http/pprof"

Additionally, the blank identifier helps when implementing an interface without explicitly using all methods:

var _ io.Reader = (*MyReader)(nil) // compilation will fail if the type does not implement the interface

Trick Question

Can the blank identifier be used for permanently suppressing errors? Is this a safe practice?

Answer: No. While the blank identifier allows you to ignore an error, this is not a safe practice — suppressing errors often leads to serious bugs or incorrect program behavior. You should always consciously handle errors and use the blank identifier to suppress them only in obvious places (e.g., explicitly insignificant to the logic).

Examples of real errors due to misunderstanding the nuances of the topic

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Story

In a file-handling application, the developer used the construct _, _ = file.Write(...) everywhere, ignoring write errors. As a result, when the disk was full or a write failed, the program continued to run "as if everything was fine," leading to data loss.

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Story

In an audit tracking project, the auditor believed that if a function returned an error, it should always be suppressed (_). Because of this, errors during logging were not noticed during testing — important data was lost, and the reason was unclear.

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Story

A student, learning Go, used the blank identifier when importing several third-party packages, although it was not necessary at all. As a result, the size of the binary file increased almost twofold, since all side effect packages were included in the final application.