Language features

Type system

Go has no type hierarchies. There are no classes, no parent-child relationships, and no inheritance. Polymorphism is achieved with interfaces.

Composition over inheritance

Go uses struct embedding instead of inheritance. Embedding places one struct type inside another, and the outer type can access the inner type’s fields and methods directly, as if they were its own.

The hlog.Interceptor from the linkd project is a practical example. It needs to behave like an http.ResponseWriter — forwarding all standard methods — but intercept WriteHeader to capture the status code:

type Interceptor struct {
    http.ResponseWriter          // all ResponseWriter methods promoted to Interceptor
    OnWriteHeader func(code int)
}

func (ic *Interceptor) WriteHeader(code int) {
    if ic.OnWriteHeader != nil {
        ic.OnWriteHeader(code)   // capture the status code
    }
    ic.ResponseWriter.WriteHeader(code) // then delegate to the original
}

Interceptor embeds http.ResponseWriter and gets Header(), Write(), and all other methods for free. It only defines WriteHeader to add behavior before delegating. No inheritance is involved. Interceptor is not a subtype of http.ResponseWriter. It satisfies the same interface because it has all the required methods.

Address space

The address space is the set of virtual memory addresses your program can use, managed by the OS and the Go runtime. Every process gets its own virtual address space from the OS, so addresses in one program are completely isolated from addresses in another.

Memory regions

The Go runtime manages memory inside your program’s address space:

The garbage collector traces pointers across the heap and frees memory that is no longer reachable.

Pointers and memory safety

A pointer (*T) is an address within your program’s address space. Go prevents you from constructing arbitrary addresses and dereferencing them. Unlike C, you cannot cast an integer to a pointer and read memory at will. If your program accesses memory outside its address space, the OS terminates it with a segmentation fault.