For the numeric types, the following sizes are guaranteed:

type                                 size in bytes

byte, uint8, int8                     1
uint16, int16                         2
uint32, int32, float32                4
uint64, int64, float64, complex64     8
complex128                           16
For the numeric types, the following sizes are guaranteed:

type                                 size in bytes

byte, uint8, int8                     1
uint16, int16                         2
uint32, int32, float32                4
uint64, int64, float64, complex64     8
complex128                           16
The built-in package unsafe, known to the compiler and accessible through the import path "unsafe", provides facilities for low-level programming including operations that violate the type system. A package using unsafe must be vetted manually for type safety and may not be portable. The package provides the following interface:

package unsafe

type ArbitraryType int  // shorthand for an arbitrary Go type; it is not a real type
type Pointer *ArbitraryType

func Alignof(variable ArbitraryType) uintptr
func Offsetof(selector ArbitraryType) uintptr
func Sizeof(variable ArbitraryType) uintptr

type IntegerType int  // shorthand for an integer type; it is not a real type
func Add(ptr Pointer, len IntegerType) Pointer
func Slice(ptr *ArbitraryType, len IntegerType) []ArbitraryType
Computer architectures may require memory addresses to be aligned; that is, for addresses of a variable to be a multiple of a factor, the variable's type's alignment. The function Alignof takes an expression denoting a variable of any type and returns the alignment of the (type of the) variable in bytes. For a variable x:

uintptr(unsafe.Pointer(&x)) % unsafe.Alignof(x) == 0
A Pointer is a pointer type but a Pointer value may not be dereferenced. Any pointer or value of underlying type uintptr can be converted to a type of underlying type Pointer and vice versa. The effect of converting between Pointer and uintptr is implementation-defined.

var f float64
bits = *(*uint64)(unsafe.Pointer(&f))

type ptr unsafe.Pointer
bits = *(*uint64)(ptr(&f))

var p ptr = nil
The function Slice returns a slice whose underlying array starts at ptr and whose length and capacity are len. Slice(ptr, len) is equivalent to

(*[len]ArbitraryType)(unsafe.Pointer(ptr))[:]
The function Offsetof takes a (possibly parenthesized) selector s.f, denoting a field f of the struct denoted by s or *s, and returns the field offset in bytes relative to the struct's address. If f is an embedded field, it must be reachable without pointer indirections through fields of the struct. For a struct s with field f:

uintptr(unsafe.Pointer(&s)) + unsafe.Offsetof(s.f) == uintptr(unsafe.Pointer(&s.f))
The following character sequences represent operators (including assignment operators) and punctuation:

+    &     +=    &=     &&    ==    !=    (    )
-    |     -=    |=     ||    <     <=    [    ]
*    ^     *=    ^=     <-    >     >=    {    }
/    <<    /=    <<=    ++    =     :=    ,    ;
%    >>    %=    >>=    --    !     ...   .    :
     &^          &^=          ~
Each type T has an underlying type: If T is one of the predeclared boolean, numeric, or string types, or a type literal, the corresponding underlying type is T itself. Otherwise, T's underlying type is the underlying type of the type to which T refers in its declaration. For a type parameter that is the underlying type of its type constraint, which is always an interface.

type (
	A1 = string
	A2 = A1
)

type (
	B1 string
	B2 B1
	B3 []B1
	B4 B3
)

func f[P any](x P) { … }
Given the declarations

type (
	A0 = []string
	A1 = A0
	A2 = struct{ a, b int }
	A3 = int
	A4 = func(A3, float64) *A0
	A5 = func(x int, _ float64) *[]string

	B0 A0
	B1 []string
	B2 struct{ a, b int }
	B3 struct{ a, c int }
	B4 func(int, float64) *B0
	B5 func(x int, y float64) *A1

	C0 = B0
	D0[P1, P2 any] struct{ x P1; y P2 }
	E0 = D0[int, string]
)
the function calls and communication happen in the order f(), h(), i(), j(), <-c, g(), and k(). However, the order of those events compared to the evaluation and indexing of x and the evaluation of y is not specified.

a := 1
f := func() int { a++; return a }
x := []int{a, f()}            // x may be [1, 2] or [2, 2]: evaluation order between a and f() is not specified
m := map[int]int{a: 1, a: 2}  // m may be {2: 1} or {2: 2}: evaluation order between the two map assignments is not specified
n := map[int]int{a: f()}      // n may be {2: 3} or {3: 3}: evaluation order between the key and the value is not specified

Recommend

The Go Programming Language Specification System considerations Package unsafe

The Go Programming Language Specification Run-time panics

The Go Programming Language Specification Errors

The Go Programming Language Specification Program initialization and execution Program execution

The Go Programming Language Specification Program initialization and execution Package initialization

The Go Programming Language Specification Program initialization and execution The zero value

The Go Programming Language Specification Packages An example package

The Go Programming Language Specification Packages Import declarations

The Go Programming Language Specification Packages Package clause

The Go Programming Language Specification Packages Source file organization

The Go Programming Language Specification Built-in functions Bootstrapping

The Go Programming Language Specification Built-in functions Handling panics

The Go Programming Language Specification Built-in functions Manipulating complex numbers

The Go Programming Language Specification Built-in functions Deletion of map elements

The Go Programming Language Specification Built-in functions Appending to and copying slices

The Go Programming Language Specification Built-in functions Making slices, maps and channels

The Go Programming Language Specification Built-in functions Allocation

The Go Programming Language Specification Built-in functions Length and capacity

The Go Programming Language Specification Statements Defer statements

The Go Programming Language Specification Statements Fallthrough statements

The Go Programming Language Specification Statements Goto statements

The Go Programming Language Specification Statements Continue statements

The Go Programming Language Specification Statements Break statements

The Go Programming Language Specification Statements Return statements

The Go Programming Language Specification Statements Select statements

The Go Programming Language Specification Statements Go statements

The Go Programming Language Specification Statements For statements For statements with range clause

The Go Programming Language Specification Statements For statements For statements with for clause

The Go Programming Language Specification Statements For statements For statements with single condition

The Go Programming Language Specification Statements For statements

The Go Programming Language Specification Statements Switch statements Type switches

The Go Programming Language Specification Statements Switch statements Expression switches

The Go Programming Language Specification Statements Switch statements

The Go Programming Language Specification Statements If statements

The Go Programming Language Specification Statements Assignments

The Go Programming Language Specification Statements IncDec statements

The Go Programming Language Specification Statements Send statements

The Go Programming Language Specification Statements Expression statements

The Go Programming Language Specification Statements Labeled statements

The Go Programming Language Specification Statements Empty statements

The Go Programming Language Specification Statements

The Go Programming Language Specification Expressions Order of evaluation

The Go Programming Language Specification Expressions Constant expressions