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Go’s built-in types are predeclared and available in all packages without import. These types form the foundation of Go’s type system.

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Boolean Type

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bool

The set of boolean values.
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bool
bool
required
Boolean type with two possible values: true and false.
var isValid bool = true
var isComplete bool = false

// Used in conditions
if isValid {
    fmt.Println("Valid")
}

// Result of comparisons
isEqual := (5 == 5)  // true
isGreater := (3 > 5) // false

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Numeric Types

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Integer Types

Go provides signed and unsigned integer types in various sizes.
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int8
int8
Signed 8-bit integer.Range: -128 to 127
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int16
int16
Signed 16-bit integer.Range: -32,768 to 32,767
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int32
int32
Signed 32-bit integer.Range: -2,147,483,648 to 2,147,483,647
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int64
int64
Signed 64-bit integer.Range: -9,223,372,036,854,775,808 to 9,223,372,036,854,775,807
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int
int
Platform-dependent signed integer type, at least 32 bits.Size: 32 bits on 32-bit systems, 64 bits on 64-bit systems
var a int8 = 127
var b int16 = 32767
var c int32 = 2147483647
var d int64 = 9223372036854775807
var e int = 42 // Most commonly used
int and uint are distinct types from their sized variants (e.g., int is not an alias for int32 or int64).

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Floating-Point Types

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float32
float32
IEEE 754 32-bit floating-point number.Precision: ~6-7 decimal digits
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float64
float64
IEEE 754 64-bit floating-point number.Precision: ~15-16 decimal digits
var f32 float32 = 3.14159265
var f64 float64 = 3.141592653589793

// Scientific notation
var big = 1.23e9    // 1.23 × 10^9
var small = 1.23e-9 // 1.23 × 10^-9

// Special values
var inf = math.Inf(1)  // Positive infinity
var nan = math.NaN()   // Not a number
Use float64 by default unless you have a specific reason to use float32. Most math operations return float64.

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Complex Types

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complex64
complex64
Complex number with float32 real and imaginary parts.
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complex128
complex128
Complex number with float64 real and imaginary parts.
var c64 complex64 = 3 + 4i
var c128 complex128 = complex(3.0, 4.0)

// Operations
sum := c128 + (1 + 2i)
product := c128 * (2 + 0i)

// Extract parts
realPart := real(c128)  // 3.0
imagPart := imag(c128)  // 4.0

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String Type

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string

Immutable sequence of bytes, conventionally UTF-8 encoded text.
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string
string
required
Sequence of 8-bit bytes. May be empty but never nil. Values are immutable.
var s string = "Hello, 世界"

// Length in bytes (not characters)
len(s) // 13 ("Hello, " is 7 bytes, "世界" is 6 bytes)

// Indexing returns bytes
firstByte := s[0] // 'H' (byte)

// Concatenation
greeting := "Hello" + " " + "World"

// Substring
sub := s[0:5] // "Hello"

// Raw string literals
path := `C:\Users\Name\file.txt` // No escape sequences

// Multi-line strings
multi := `Line 1
Line 2
Line 3`
Indexing a string returns bytes, not characters. Use range or the unicode/utf8 package for proper Unicode handling.
s := "Hello"
for i := 0; i < len(s); i++ {
    fmt.Printf("%c ", s[i]) // H e l l o
}

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Type Aliases

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byte

Alias for uint8. Used to distinguish byte values from 8-bit integers.
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byte
uint8
required
Equivalent to uint8 in all ways. Used by convention for raw binary data.
var b byte = 255
var bytes []byte = []byte("Hello")

// Reading files returns []byte
data, err := os.ReadFile("file.txt")

// Convert between string and []byte
s := string(bytes)     // []byte to string
bytes = []byte(s)      // string to []byte

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rune

Alias for int32. Used to distinguish character values from integers.
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rune
int32
required
Equivalent to int32 in all ways. Represents a Unicode code point.
var r rune = '世' // Single quotes for rune literals
var r2 rune = 0x4E16 // Unicode code point

// Convert string to runes
s := "Hello, 世界"
runes := []rune(s)
fmt.Println(len(runes)) // 9 (character count)

// Character literals
var newline rune = '\n'
var tab rune = '\t'
var unicode rune = '\u4E16' // Unicode escape
Use rune when working with Unicode characters. Use byte when working with binary data or ASCII.

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any

Alias for interface{}. Represents any type.
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any
interface{}
required
Equivalent to interface{} in all ways. Can hold values of any type.
var a any = 42
var b any = "hello"
var c any = []int{1, 2, 3}

// Type assertion
if str, ok := a.(string); ok {
    fmt.Println("String:", str)
}

// Type switch
switch v := a.(type) {
case int:
    fmt.Println("Integer:", v)
case string:
    fmt.Println("String:", v)
default:
    fmt.Println("Unknown type")
}

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Special Types

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comparable

Interface implemented by all comparable types.
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comparable
interface{ comparable }
required
Constraint for types that support == and != operators.Can only be used as a type parameter constraint, not as a variable type.
// Valid: type parameter constraint
func Equal[T comparable](a, b T) bool {
    return a == b
}

fmt.Println(Equal(5, 5))           // true
fmt.Println(Equal("a", "b"))       // false
fmt.Println(Equal(3.14, 3.14))     // true

// Invalid: cannot use as variable type
// var x comparable = 42 // Compile error
Comparable types include booleans, numbers, strings, pointers, channels, arrays of comparable types, and structs whose fields are all comparable.

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error

Conventional interface for representing errors.
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error
interface
required
Interface with a single Error() string method.The nil value represents no error.
type error interface {
    Error() string
}

import "errors"

err := errors.New("something went wrong")
err := fmt.Errorf("failed to process %s", filename)
Always check error values. The Go convention is to return errors as the last return value and check them immediately.

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Documentation Types

These types appear in the builtin package for documentation purposes only.
Stand-in for any Go type in function signatures. Represents the same type within a function invocation.Not a real type; used only in documentation.
Stand-in for a second distinct Go type in function signatures.Not a real type; used only in documentation.
Stand-in for either a Go type or an expression in function signatures.Not a real type; used only in documentation.
Stand-in for any integer type: int, uint, int8, int16, int32, int64, uint8, uint16, uint32, uint64, uintptr.Not a real type; used only in documentation.
Stand-in for either float32 or float64.Not a real type; used only in documentation.
Stand-in for either complex64 or complex128.Not a real type; used only in documentation.

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Type Conversion

// Numeric conversions
var i int = 42
var f float64 = float64(i)
var u uint = uint(i)

// String conversions
var s string = string([]byte{'h', 'e', 'l', 'l', 'o'})
var b []byte = []byte("hello")
var r []rune = []rune("hello")

// Rune to string
var ch rune = '世'
var str string = string(ch)
Converting between numeric types may change the value. Converting a larger type to a smaller type may truncate or overflow.

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