Go Concepts - Lexical Structure

Internal

• Go Concepts

Source Files

Go code goes into source files. They have the .go extension.

Each source file is mandatory declared to belong to a package.

They can then optionally import code from other packages, using the import keyword.

Comments

// to the end of the line

/*
  Multiline
  line 1
  ...
  line n
*/

Whitespace

Whitespace in Go are carriage returns (u+000D), newlines (u+000A), spaces (u+0020) and tabs (u+0009).

Semicolons

Go programs may omit most of the semicolons at the end of line if the following conditions apply:

1. When the input is broken into tokens, a semicolon is automatically inserted into the token stream immediately after a line's final token if that token is:
   1. an identifier
   2. an integer, floating-point, imaginary, rune, or string literal
   3. one of the keywords break, continue, fall through, or return
   4. one of the operators and delimiters ++, --, ), ], or }
2. To allow complex statements to occupy a single line, a semicolon may be omitted before a closing ")" or "}".

For more details, see the specification:

https://golang.org/ref/spec#Semicolons

Identifiers

Identifiers name program entities, such as constants, variables, types, functions, etc. An identifier is a sequence of one more letter and digits. The first character must be a letter. The letters are unicode letters or underscore "_".

Pre-Declared Identifiers

Pre-declared identifiers are available by default, without needing to import anything. They are implicitly declared in the universe block.

Pre-declared types: bool, byte, complex64, complex128, float32, float64, int, int8, int16, int32, int64, rune, string, uint, uint8, uint16, uint32, uint64, uintptr and error.

Pre-declared constants: true, false, iota.

Pre-declared functions: append, cap, close, complex, copy, delete, imag, len, make, new, panic, print, println, real, recover. Also see built-in functions.

Pre-declared zero value: nil.

The blank identifier "_".

Identifiers (not values) can be exported or unexported.

Lower-case letter identifiers

Upper-case letter identifiers

Types

The Type System

Functions

Functions

Operators

Operators

Expression

Operators combine operands into expressions.

Literal

A literal is a notation for representing a fixed value in source code. Go provides literals for booleans, integers, floating-point values, strings, built-in types such as arrays, slices and maps, user-defined types (structs), functions, etc.

Statements

• Go Language Specification https://golang.org/ref/spec#Statements

Statements control execution flow within a function.

Keywords

• Go Specification - Keywords: https://golang.org/ref/spec#Keywords

range	type	func	.	.
package	go	.	.	.
defer	chan	import	.	.

Variables

Variables are always initialized to the type's zero value.

  var <var-name> <type> = <initial-value>

  var a string = "blah"

  <var-name> := <initial-value>

   a := "blah"

Variable Scopes

Package-level variable

Pass by Value vs Pass by Reference

In Go, all variables are passed by value. Even for pointer variables, since the value of the pointer is a memory address, passing pointer variables is still considered pass by value.

Pointers

Pointer variable.