Go ':=' vs. '=': When to Use Short Variable Declarations?

Understanding the Distinction between ":=" and "=" in Go

As a novice in Go, you might be perplexed by the seemingly interchangeable use of ":=" and "=" for variable assignments. However, there is a subtle difference that revolves around the context of variable declarations.

The Role of "="

In Go, "=" is primarily employed for variable assignments. It adheres to the syntax of "var name type = expression," where "name" represents the variable being assigned. Crucially, the type or the assignment expression can be omitted, but not both.

The Nature of ":="

In contrast, ":=" denotes short variable declaration, which follows the format "name := expression." Here, the ":=" acts as a combined declaration and assignment operator. The type of "name" is automatically inferred from the type of "expression."

Distinguishing Between Declaration and Assignment

The key difference lies in the primary purpose of each operator. ":=" is solely for declaration, whereas "=" is used for assignment. Therefore, short variable declarations must invariably introduce at least one entirely new variable within the current lexical block.

Examples of Usage

To illustrate the distinction, consider the following examples:

1.   var x int = 1

   This statement declares an integer variable "x" and initializes it with the value 1.

2.   r := foo()

   This is a short variable declaration that assigns the return value of the "foo()" function to the newly created variable "r."

This creates a new variable "m" and assigns a new value to the existing variable "r."

**Exceptions and Additional Information**

It's worth noting that ":=" can only be used within functions. However, it can declare temporary variables within the initializers of control structures like "if," "for," and "switch."

For further exploration, you can refer to the official Go documentation on:

* [Variable Declarations](https://go.dev/ref/spec#Variable_declarations)

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