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2. Program Structure

Predeclared Names

Keywords

  • break
  • case
  • chan
  • const
  • continue
  • default
  • defer
  • else
  • fallthrough
  • for
  • func
  • go
  • goto
  • if
  • import
  • interface
  • map
  • package
  • range
  • return
  • select
  • struct
  • switch
  • type
  • var

Constants

  • true
  • false
  • iota
  • nil

Types

  • int
  • int8
  • int16
  • int32
  • int64
  • unit
  • unit8
  • unit16
  • unit32
  • uint64
  • uintptr
  • float32
  • float64
  • complex128
  • complex64
  • bool
  • byte
  • rune
  • string
  • error

Functions

  • make
  • len
  • cap
  • new
  • append
  • copy
  • close
  • delete
  • complex
  • real
  • imag
  • panic
  • recover

Variables

  • There are no uninitialized variables (no assignment defaults to zero-value).
  • Note do not confuse short, multi-variable declarations with tuple assignments (:= vs =)
  • Short multi-variable assignments will assign to variables already declared. (scope is important)
    • but a short variable dec must have at least one declaration for this to work.
    • so just use ordinary assignment (=) if no new declarations
  • Style: avoid tuple assignments if complicated expressions/hinders readability

Pointers

  • Pointers and addresses (* and &) same as in C lang. Except cannot do pointer arithmetic.

Var Lifetimes

  • Package-level variable lifetime is entire execution of program
  • Local variables have dynamic lifetimes: new instance is created each time declaration statement is executed and lives until out of scope/unreachable

Assertions

  1. Map lookup: v, ok = m[key]
  2. Type assertion: v, ok = x.(T)
  3. Channel receive: v, ok = <-ch

Assignability

Types

  • Assignability and comparisons vary by type.
  • type declarations: type name underlying-type

Packages & Files

  • Each package serves as a separate name space for its declaration.
  • Exported (public) identifiers start with uppercase letter.
  • Doc comments are placed immediately before package declarations.
  • By convention, import name should match the leaf of import path.
  • Package-level variables are initialized in order they were declared in (note package names sorted before compiling)
  • Packages resolve dependencies before importing. (if p imports q, q must be fully resolved first).
  • init functions in packages are executed when the program starts. Thus, all packages init functions are run before main.

Scope

  • Lexical blocks ({})
  • Style: handle error in if block, so successful execution path is not indented.