Why Does Go Use `:=` for Assignment Instead of `=`?

Go Language Assignment Operator: Demystifying the Colon

In Go, the assignment operator is often written with a colon before the equal sign, e.g., :=. This notation differs from other programming languages where = is the sole assignment operator.

Why the Unique Notation?

The := operator serves a double purpose: declaration and initialization. Consider the following code:

name := "John"

This statement simultaneously declares a variable named name and initializes it with the value "John." In other words, it is equivalent to:

var name = "John"

The := syntax helps avoid common typographical errors. For instance, in the following code, it's unclear whether fooo is a new variable or a typo of foo:

foo = "bar"
fooo = "baz" + foo + "baz"

Avoiding Misinterpretations

By using := to declare and initialize variables, Go ensures that the code is clear and easy to understand. It eliminates the potential for accidental variable redeclarations or incorrect assignments.

Furthermore, := simplifies type inference in Go. For example:

foo := 123

When using :=, the compiler can automatically infer that foo is an integer. In contrast, if one used foo = 123, the compiler would require the programmer to specify foo's type explicitly (e.g., var foo int = 123).

Additional Note

The := operator is used only for variable declaration and initialization. If you need to assign a new value to an existing variable, the standard assignment operator = is used.

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