In dynamic languages, programmers don't need to explicitly declare variable types and think about the types in advance. This means you can use variables of any type in functions and expressions without strict type checking and rely on what's called duck typing. Programs written in dynamic languages are usually interpreted.
For example, consider the sum_of_two function in Python.
It can effortlessly handle various types of inputs, whether they're integers, floats, strings or even lists:
def sum_of_two(number1, number2):
return number1 + number2
>>> sum_of_two(3, 4)
7
>>> sum_of_two(3.3, 4.4)
7.7
>>> sum_of_two(2, 3.3)
5.3
>>> sum_of_two("3", "4")
'34'
>>> sum_of_two([1, 2, 3], [5, 6, 7])
[1, 2, 3, 5, 6, 7]
While this flexibility allows for creative solutions, it also places the responsibility on the programmer to ensure that types are used correctly.
Other famous dynamic languages: JavaScript, PHP, Ruby, Lua.
On the other hand, in static languages you must explicitly declare variable types, and the compiler enforces strict type checking. This means you can't pass a variable of the wrong type to a function or expression without encountering an error. Programs written in static languages are usually compiled (or transpiled).
Take the sumTwo function in Go as an example:
func sumTwo(number1 int, number2 int) int {
return number1 + number2
}
// sum_two.go
func main() {
fmt.Println(sumTwo(3, 4))
}
$ go run sum_two.go
7
// sum_two.go
func main() {
fmt.Println(sumTwo(3.4, 4.3))
}
$ go run sum_two.go
./sum_two.go:10:28: constant 3.4 truncated to integer
./sum_two.go:10:33: constant 4.3 truncated to integer
// sum_two.go
func main() {
fmt.Println(sumTwo("3", "4"))
}
$ go run sum_two.go
./sum_two.go:10:28: cannot use "3" (type untyped string) as type int in argument to sumTwo
./sum_two.go:10:33: cannot use "4" (type untyped string) as type int in argument to sumTwo
It only accepts integers, and attempting to pass it a float or a string will result in a compile-time error. While this approach may seem more restrictive, it offers greater assurance that your code is type-safe and free from certain classes of errors.
Other famous static languages: Java, TypeScript, Swift, Rust.