Reading JSON Files as Object in Go
In Go, you can encounter difficulties when attempting to read a JSON file and parse it as a JSON object.
Failed Attempts
Some failed attempts to read JSON files as objects include:
plan, _ := ioutil.ReadFile(filename) // filename is the JSON file to read var data interface{} err := json.Unmarshal(plan, data)
This results in the error "json: Unmarshal(nil)".
generatePlan, _ := json.MarshalIndent(plan, "", " ") // plan is a pointer to a struct
This produces a string output, but casting it to a string makes it impossible to loop through as a JSON object.
Solution
The key to resolving this issue lies in the value pointed to by json.Unmarshal. It must be a pointer.
plan, _ := ioutil.ReadFile(filename) var data interface{} err := json.Unmarshal(plan, &data)
Type Assertion
When using an empty interface in unmarshal, you need to use type assertion to get underlying values as native Go types:
bool, for JSON booleans float64, for JSON numbers string, for JSON strings []interface{}, for JSON arrays map[string]interface{}, for JSON objects nil for JSON null
Best Practice
It's highly recommended to use a concrete structure to populate JSON data using Unmarshal. This provides better clarity and avoids the need for type assertions.
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