Struct tags in Go

A tag is metadata on a field, read by reflection at run time.

type Run struct {
    Lang     string    `json:"lang"`
    TPM      float64   `json:"tpm"`
    Stars    int       `json:"stars,omitempty"`
    Note     string    `json:"-"`
    Recorded time.Time `json:"recorded_at"`
}

func encode() (string, error) {
    run := Run{Lang: "go", TPM: 104.5, Note: "private"}
    data, err := json.Marshal(run)
    if err != nil {
        return "", fmt.Errorf("marshal: %w", err)
    }
    return string(data), nil
}

How it works

1. The convention is key:\u0022value,option\u0022 per encoder.
2. json:\u0022-\u0022 omits a field entirely.
3. omitempty drops the field when it holds its zero value.

Keywords and builtins used here

• error
• float64
• func
• if
• int
• return
• string
• struct
• type

The run, in numbers

Lines

16

Characters to type

401

Tokens

83

Three-star pace

105 tpm

At the three-star pace of 105 tokens a minute, this run takes about 47 seconds.

Type this snippet

Step 2 of 5 in Packages & build, step 22 of 26 in Standard library & project layout.

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