Code Examples

JavaScript

// JavaScript is dynamically typed
// variables need not be declared
// before use
x = undefined;  // undefined
x = true;       // boolean
x = 3;          // number
x = NaN;        // number
x = Infinity;   // number
x = "3";        // string
x = () => {};   // function
x = null;       // object
x = [];         // object
x = {};         // object
x = new Date(); // object

Primitive Types

• undefined
• boolean
• number
• string

Object types

• object
• function   
• array
• null

See this survey by Douglas Crockford for a good overview

PYthon

# Python is dynamically typed; variables
# do not need to be declared before use
x = True        # bool
x = "hi"        # str
x = 3           # int
x = 3.0         # float
x = 3j          # complex
x = None        # NoneType (null value)
x = [1, 2, 3]   # list (an array)
x = (1, 2, 3)   # tuple (immutable list)
x = {1, 2, 3}   # set
x = {"one": 1}  # dict (a hash table)
x = lambda x: x # function
x = b"hello"    # bytes (binary data)

• Everything is an object
• Every expression has a boolean value
• Important types:
  • boolean
  • number
  • string
  • byte
  • list
  • tuple
  • set
  • dictionary

See description of native types in DiveIntoPython3 for a good overview

R

> # R is dynamically typed; variables do not
> # need to be declared before using them
> x <- 5.25             # numeric
> x <- 5                # numeric
> is.integer(x)         # FALSE
> x <- as.integer(5)    # integer
> is.integer(x)         # TRUE
> x <- 1 + 2i           # complex
> x <- TRUE             # logical
> x <- "hello"          # character
> x <- c(1, 2, 3)       # numeric vector (array)
> x <- c("1", "2", "3") # character vector

> x <- matrix(c(1,2,3,4), nrow=2,
              ncol=2, byrow=TRUE)
> x                     # matrix (2D array)
     [,1] [,2]
[1,]    1    2
[2,]    3    4

> x <- list(c(1, 2, 3), # list (array of vectors)
        c("1","2","3"))

> # data frames are special and unique to R
> # and worthy of study on their own

• Everything is an object
• Important types:
  • numeric
  • integer
  • complex
  • logical
  • character
  • vector (array)
  • matrix (2D array)
  • list
  • data frame

See this R Tutorial for a good overview

Ruby

# Ruby is dynamically typed; variables
# do not need to be declared before use
x = nil                  # Nil (null)
x = true                 # Boolean
x = 5                    # Integer
x = 5.0                  # Float
x = "hello"              # String
x = [1, 2, 3]            # Array
x = {"one": 1, "two": 2} # Hash
x = :x                   # Symbol

# all looks pretty standard except Symbol...
# what the hell is Symbol?

• Everything is an object
• Primary types:
  • Nil
  • Boolean
  • Numeric
    • Integer
    • Float
  • String
  • Array
  • Hash
  • Symbol

See this wikibook for a good overview (including an explanation of the mysterious Symbol type)

PHP

# PHP is dynamically typed; variables
# do not need to be declared before use
$x = null;                  # NULL
$x = true;                  # boolean
$x = 5;                     # integer
$x = 5.0;                   # double
$x = 'hello';               # string
$x = [1, 2, 3];             # array
$x = (object) ["one" => 1]; # object
$x = fopen('x.txt', 'w');   # resource

# a resource is something like a file
# reference or a network or database
# connection

• Types:
  • NULL
  • Boolean
  • Integer
  • Double
  • String
  • Array
  • Object
  • Resource

W3Schools has good tutorials on most things, and their PHP data type overview is no exception

Java

class Main {
  public static void main(String[] args) {
    byte    y = 0;    //  8-bit int: +/- 2^7
    short   s = 1;    // 16-bit int: +/- 2^15
    int     i = 2;    // 32-bit int: +/- 2^31
    long    l = 3;    // 64-bit int: +/- 2^63
    float   f = 4.0f; // 32-bit precision
    double  d = 5.1;  // 64-bit precision
    boolean b = true; //  1-bit
    char    c = 'a';  // 16-bit unicode char
    String hi = "hi"; // equivalent to below
    char[] h2 = {'h', 'i'}; // array of char
  }
}

• Primitive Types:
  • Integers
    • byte
    • short
    • int
    • long
  • Floating Points
    • float
    • double
  • boolean
  • char

The Java™ Tutorial is the official place to read up on this

Go

package main
import "fmt"
func main() {
  var // indicates we're starting our 
      // variable declarations
  bool    b = true // 1-bit boolean
  string hi = "hi" // string
  // unsigned integers
  ui   uint   = 0   // 32 or 64 bit
  ui8  uint8  = 0   //  8-bit: 0 ~ 255
  ui16 uint16 = 0   // 16-bit: 0 ~ 2^16
  ui32 uint32 = 0   // 32-bit: 0 ~ 2^32
  ui64 uint64 = 0   // 64-bit: 0 ~ 2^64
  y    byte   = 0   // alias for uint8
  // signed integers
  ui   int    = 0   // same as uint
  ui8  int8   = 0   //  8-bit: +/- 2^7
  ui16 int16  = 0   // 16-bit: +/- 2^15
  ui32 int32  = 0   // 32-bit: +/- 2^31
  ui64 int64  = 0   // 64-bit: +/- 2^63
  rn   rune   = 0   // alias for int32
  // floats
  f32 float32 = 4.0 // 32-bit precision
  f64 float64 = 4.0 // 64-bit precision
  // complex numbers: 64- and 128-bit
  c64   complex64 = (1.0 + 2i)
  c128 complex128 = (1.0 + 2i)
}

In addition to the types shown to the right, Go has:

• Array
• Struct
• Pointer
• Function
• Interface
• Slice
• Map
• Channel

Try this tutorial if you're interested