Why is my Go struct not decoding JSON correctly?

Decoding JSON into a Go Struct

In Go, parsing a JSON file into a struct requires the use of the encoding/json package. However, incorrect JSON structure parsing can lead to unexpected results.

Consider the code snippet provided below:

var settings struct {
    serverMode bool
    sourceDir  string
    targetDir  string
}

func main() {
    // ...
}

With the JSON configuration file:

{
    "serverMode": true,
    "sourceDir": ".",
    "targetDir": "."
}

You may encounter a puzzling output:

false  
(false and two empty strings)

This issue arises because the struct elements are not exported. By default, struct elements beginning with a lowercase letter are invisible to the JSON encoder/decoder. To resolve this, export the struct elements by capitalizing their first letters:

var settings struct {
    ServerMode bool `json:"serverMode"`
    SourceDir  string `json:"sourceDir"`
    TargetDir  string `json:"targetDir"`
}

Exporting the struct elements ensures that the JSON encoder/decoder can access and decode the struct values. This will result in the correct parsing of the JSON configuration file into the struct.

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