KITFORMA · EDITORIAL GUIDE
How do I preserve a large JSON integer in a generic Go object?
KitForma editorial guide. Generic decoding into float64 can lose integer precision before the application inspects the value. Casting a rounded float back cannot restore original digits.
Step-by-step guidance
Generic decoding into float64 can lose integer precision before the application inspects the value. Casting a rounded float back cannot restore original digits.
Use a typed integer field for a known schema, or Decoder.UseNumber:
package main
import ("encoding/json"; "fmt"; "strings")
func main() {
d := json.NewDecoder(strings.NewReader(`{"id":9007199254740993}`))
d.UseNumber()
var value map[string]any
if err := d.Decode(&value); err != nil { panic(err) }
fmt.Println(value["id"].(json.Number).String())
}Expected digits remain unchanged. The fixture assumes a known shape; production must check type, range and trailing input. Preserving textual digits is not complete schema validation.
Sources and verification
Sources checked:
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