I walk through the "Writing Useful go/analysis Linter" tutorial by Denis Isaev, and build my first linter from scratch.

Type definitions … A generic type may also have methods associated with it. In this case, the method receivers must declare the same number of type parameters as present in the generic type definition. // The method Len returns the number of elements in the linked list l. func (l *List[T]) Len() int { … } This probably needs further explanation. Or an example. It did for me. Let’s look at a simple generic type:

There’s a lot to cover within type definitions! We’re several days in, and still going strong… Type definitions … In a type definition the given type cannot be a type parameter. type T[P any] P // illegal: P is a type parameter func f[T any]() { type L T // illegal: T is a type parameter declared by the enclosing function } I expect this will surprise noone. We’ve already seen that struct, array, and slice types cannot reference themselves.

Type definitions … If the type definition specifies type parameters, the type name denotes a generic type. Generic types must be instantiated when they are used. type List[T any] struct { next *List[T] value T } We haven’t covered instantiation yet, but we will. For now, let’s just summarize: Instantiation is process by which a generic type’s type parameters are substituted with the actual type arguments to be used.

I’ll be livestreaming again today, in just a few minutes. Join me live, or watch the replay. I’ll be picking up where I left off, with my new linter project. One of the most powerful things I like about Go, is the ability to put methods on any type. Type definitions … Type definitions may be used to define different boolean, numeric, or string types and associate methods with them:

Type definitions … A defined type may have methods associated with it. It does not inherit any methods bound to the given type, but the method set of an interface type or of elements of a composite type remains unchanged: // A Mutex is a data type with two methods, Lock and Unlock. type Mutex struct { /* Mutex fields */ } func (m *Mutex) Lock() { /* Lock implementation */ } func (m *Mutex) Unlock() { /* Unlock implementation */ } // NewMutex has the same composition as Mutex but its method set is empty.

Some of the minutiae we’ve gone over about underlying types, and type identity are finally starting to come together… Type definitions A type definition creates a new, distinct type with the same underlying type and operations as the given type and binds an identifier, the type name, to it. TypeDef = identifier [ TypeParameters ] Type . The new type is called a defined type. It is different from any other type, including the type it is created from.

Listen as I discuss Go, DevOps, and more, with Lane Wagner on the Backend Banter podcast.

Alias declarations An alias declaration binds an identifier to the given type. AliasDecl = identifier "=" Type . Within the scope of the identifier, it serves as an alias for the type. type ( nodeList = []*Node // nodeList and []*Node are identical types Polar = polar // Polar and polar denote identical types ) Aliases are a feature you likely won’t use frequently. You may never use it, in fact.

We’ve already talked about the different types availabe in Go, but now we’ll see how to declare them… just in case it wasn’t already obvious. Type declarations A type declaration binds an identifier, the type name, to a type. Type declarations come in two forms: alias declarations and type definitions. TypeDecl = "type" ( TypeSpec | "(" { TypeSpec ";" } ")" ) . TypeSpec = AliasDecl | TypeDef . We’ll talk about these two different forms in the coming days.

No live stream today. My office/recording studio is being painted. I’ll be back next week with more linter building! One last detail on iota… Iota … By definition, multiple uses of iota in the same ConstSpec all have the same value: const ( bit0, mask0 = 1 << iota, 1<<iota - 1 // bit0 == 1, mask0 == 0 (iota == 0) bit1, mask1 // bit1 == 2, mask1 == 1 (iota == 1) _, _ // (iota == 2, unused) bit3, mask3 // bit3 == 8, mask3 == 7 (iota == 3) ) This last example exploits the [implicit repetition](https://go.