Struct tag
A struct tag is metadata attached to a Go struct field that guides reflection-based processing such as serialization and field mapping.
Learn Go with Pocket-Sized Projects
A struct tag is metadata attached to a Go struct field that directs packages such as encoding/xml or encoding/json how the field maps to encoded data.
- How it is used
- Maps JSON file fields and XML response elements or attributes into Go structs for decoding.
- How deep it goes
- Explains tag syntax, exported fields, pointer destinations, XML paths and attributes; defers detailed pointer explanation.
- Examples
- Uses a bookworm JSON file and an exchange-rate XML response with nested elements and attributes.
- What you can do after
- Apply it via encoding/json and encoding/xml to decode tagged structs from a file or HTTP response.
Read how Learn Go with Pocket-Sized Projects explains struct tag →
Go in Practice, Second Edition
A struct tag is a Go field annotation containing metadata, commonly expressed as whitespace-separated key-value pairs for controlling data encoding or other processing.
- How it is used
- Controls encoded field names and supplies metadata for custom processing such as validation and name-value file mapping.
- How deep it goes
- Moves from tag syntax and JSON output to runtime tag lookup and a reflection-based encoder and decoder.
- Examples
- Uses JSON-encoded animal data, help and validation tags, and an INI-style process-data encoder and decoder.
- What you can do after
- Build it from scratch: define a custom field-tag convention and read it with `reflect` in marshaling and unmarshaling code.
Read how Go in Practice, Second Edition explains struct tag →
Go in Action, Second Edition
A struct tag is metadata attached to a Go struct field that can guide reflection-based processing such as serialization and field mapping.
- How it is used
- Maps configuration fields between Go structs and JSON or XML representations in a validation and conversion CLI.
- How deep it goes
- Defines tag metadata and works through JSON and XML mappings, including options and XML-specific forms; leaves specialized validation to custom methods.
- Examples
- Uses a server configuration with JSON keys, omitted fields, XML attributes and elements, and conversion between formats.
- What you can do after
- Apply it via encoding/json and encoding/xml to map one exported-field struct to both formats in a configuration converter.
Related concepts
- encoding/jsonused by · encoding/json is Go’s standard-library package for encoding Go values as JSON and decoding JSON into Go values.
- reflectionuses · Reflection is a programming capability for inspecting or interacting with program types, members, values, or metadata dynamically at runtime.
- encoding/xmlused by · encoding/xml is Go’s standard-library package for encoding Go values as XML and decoding XML data into Go values.
- JSONuses · JSON is a standardized, language-independent text format for representing structured data using objects, arrays, strings, numbers, Boolean values, and null.
- attributeconfigures · An attribute is a named property, value, or piece of information associated with an entity, object, or program element.
- xmluses · XML is a text-based markup language for encoding structured documents and data using elements, attributes, and nested relationships.
These guides are generated from the text of Manning books by Manning's knowledge graph and link to the sections they draw on. The full books are available on liveBook and at manning.com.