Blog / Go Language Spec

Slice types

March 3, 2023

So we’ve learned about the fixed-length, and therefore somewaht limited, array types. Let’s now look at the more flexible cousin, the slice.

Slice types

A slice is a descriptor for a contiguous segment of an underlying array and provides access to a numbered sequence of elements from that array. A slice type denotes the set of all slices of arrays of its element type. The number of elements is called the length of the slice and is never negative. The value of an uninitialized slice is nil.

SliceType = "[" "]" ElementType .

Okay, so what does that all mean?

It basically means that a slice can be thought of as a view into an underlying array.

Let me illustrate with an example:

	// Initialize a as an array of 10 integers
	var a = [10]int{0, 1, 2, 3, 4, 5, 6, 7, 8, 9}
	// Initialize s as a slice "view" of a, of indexes 0, 1, and 2
	var s = a[0:3]
	fmt.Println(a, s) // Prints: [0 1 2 3 4 5 6 7 8 9] [0 1 2]

See this code in the playground

Quotes from The Go Programming Language Specification, Version of January 19, 2023

Share this

Related Content

Empty structs

We finally we have enough knowledge for the EBNF format not to seem completely foreign, so let’s jump back and take a look at that, with the examples provided in the spec… Struct types … StructType = "struct" "{" { FieldDecl ";" } "}" . FieldDecl = (IdentifierList Type | EmbeddedField) [ Tag ] . EmbeddedField = [ "*" ] TypeName [ TypeArgs ] . Tag = string_lit . // An empty struct.

Struct tags

Struct types … A field declaration may be followed by an optional string literal tag, which becomes an attribute for all the fields in the corresponding field declaration. An empty tag string is equivalent to an absent tag. The tags are made visible through a reflection interface and take part in type identity for structs but are otherwise ignored. struct { x, y float64 "" // an empty tag string is like an absent tag name string "any string is permitted as a tag" _ [4]byte "ceci n'est pas un champ de structure" } // A struct corresponding to a TimeStamp protocol buffer.

Struct method promotion

Yesterday we saw an example of struct field promotion. But methods (which we haven’t really discussed yet) can also be promoted. Struct types … Given a struct type S and a named type T, promoted methods are included in the method set of the struct as follows: If S contains an embedded field T, the method sets of S and *S both include promoted methods with receiver T. The method set of *S also includes promoted methods with receiver *T.