How Can I Preserve Trailing Zeroes in Go\'s JSON Marshaling of Floating-Point Numbers?

JSON Marshaling: Preserving Trailing Zeroes in Floating-Point Numbers

When serializing data into JSON using json.Marshal() in Go, trailing zeroes in floating-point numbers are often stripped. This can be problematic when the receiving end expects floating-point values with decimal places.

Solution: Custom Marshal Function

An effective way to prevent json.Marshal() from removing the trailing zeroes is to define a custom MarshalJSON() method for the type containing the floating-point value. This allows you to manually control the serialization process.

Consider the following example:

type MyFloat float64

func (f MyFloat) MarshalJSON() ([]byte, error) {
    // Check if the float is an integer (no decimal part).
    if math.Trunc(float64(f)) == float64(f) {
        // Serialize as an integer without the trailing zero.
        return []byte(strconv.FormatInt(int64(f), 10)), nil
    }

    // Serialize as a floating-point number with the trailing zero.
    return []byte(strconv.FormatFloat(float64(f), 'f', -1, 64)), nil
}

In this example, the MyFloat type defines a custom MarshalJSON() method that checks if the float is an integer (no decimal part) and serializes it accordingly. For floating-point numbers, it serializes them with the trailing zero intact.

Usage:

Once you have defined the custom MarshalJSON() method, you can use it to serialize objects containing the MyFloat type. For instance:

type MyStruct struct {
    Value MyFloat
    Unit  string
}

// Serialize MyStruct using the custom MarshalJSON method.
data, err := json.Marshal(MyStruct{40.0, "some_string"})

This will result in the following JSON output:

{
  "Value": 40.0,
  "Unit": "some_string"
}

Note:

• The custom MarshalJSON() method must be defined on the type that will be serialized.
• If the float represents an integer (no decimal part), you can consider using an integer type instead of a float to avoid any ambiguity.

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