Stage 1 · Code

Functions & Composite Types

Structs

Group related fields into named types — Go's way to model records, entities, and domain objects without classes.

7 min readProgramming Foundations (Go)Code

Defining Structs

A struct is a composite type that groups fields together under one name. Each field has a name and a type. Structs replace classes in Go — they hold data, and you attach behaviour separately using methods.

Gostruct-definition.go

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Field names are capitalized here so they are exported (accessible from other packages). Use lowercase field names for internal-only fields. Struct type names follow the same visibility rules.

Creating and Using Structs

You can create a struct with positional or named field initialization. Named initialization is almost always preferred — it is self-documenting and unaffected by field reordering.

Gostruct-literals-and-field-access.go

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`%+v` in `fmt.Printf` prints a struct with its field names — useful for debugging. A struct declared with `var` or used as a field in another struct is automatically zeroed.

Always use named field initialization

Positional initialization Server{"host", 443, true, 1000} breaks silently when you add, remove, or reorder fields. Named initialization Server{Host: "host", Port: 443} survives field changes and is self-documenting. Make it a habit.

Struct Embedding

Embedding includes one struct type inside another without giving it an explicit field name. The embedded type's fields and methods are promoted: you can access them directly on the outer struct.

Goembedding-for-composition.go

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Embedding is **composition**, not inheritance. The outer type does not 'extend' the inner one — it includes it. You can override a promoted method by defining it on the outer type. There is no `super` or `override` keyword.

Comparing Structs

Two structs of the same type are equal if all their fields are equal. Structs that contain non-comparable fields (like maps or slices) cannot be compared with ==.

Gostruct-equality.go

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Because `Point` is comparable, it can be used as a map key. Structs containing slices or maps are not comparable and will cause a compile error if you try to use `==` on them.

Anonymous Structs

You can define a struct without giving it a name. Anonymous structs are useful for small, local data shapes — especially in tests and one-off groupings.

Goanonymous-struct-for-table-tests.go

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This pattern — a slice of anonymous structs for test cases — is the standard Go table-driven test shape. You will see it everywhere in the standard library and in real codebases.

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