Can You Use Variables in Struct Tags in Go?

Struct Tags in Go: Can Variables Be Used?

Struct tags are a powerful feature of Go that allow developers to attach metadata to fields. This metadata can be used by various tools, such as JSON encoders and decoders.

Using String Literals for Struct Tags

In the first example, you are using a string literal to define a struct tag:

<code class="go">type Shape struct {
    Type string `json:"type"`
}</code>

This is a valid approach, as the tag value is a compile-time string constant.

Attempting to Use Variables for Struct Tags

In the second example, you are trying to use a variable to define a struct tag:

<code class="go">const (
    TYPE = "type"
)

type Shape struct {
    Type string fmt.Sprintf("json:\"%s\"", TYPE)
}</code>

However, this approach will result in a syntax error because the compiler expects a string literal as the tag value. Variables cannot be used in struct tags because the tag value must be known at compile time.

Conclusion

While it may seem convenient to use variables for struct tags, the Go language does not allow this. You must use string literals to define struct tags.

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