I am new to Go programming language.
I noticed something strange in Go: I thought that it used :=
and substitutes =
in Python, but when I use =
in Go it is also works.
What is the difference between :=
and =
?
=
is assignment. more about assignment in Go: Assignments
The subtle difference between =
and :=
is when =
used in variable declarations.
General form of variable declaration in Go is:
var name type = expression
the above declaration creates a variable of a particular type, attaches a name to it, and sets its initial value. Either the type
or the = expression
can be omitted, but not both.
For example:
var x int = 1
var a int
var b, c, d = 3.14, "stackoverflow", true
:=
is called short variable declaration
which takes form
name := expression
and the type of name is determined by the type of expression
Note that: :=
is a declaration, whereas =
is an assignment
So, a short variable declaration must declare at least one new variable. which means a short variable declaration doesn't necessarily declare all the variables on its left-hand side, when some of them were already declared in the same lexical block, then :=
acts like an assignment to those variables
For example:
r := foo() // ok, declare a new variable r
r, m := bar() // ok, declare a new variable m and assign r a new value
r, m := bar2() //compile error: no new variables
Besides, :=
may appear only inside functions. In some contexts such as the initializers for "if", "for", or "switch" statements, they can be used to declare local temporary variables.
More info: