Go := vs. =: When to Use Each Assignment Operator?

Comparing the Roles of := and = in Go Programming

In Go, the := and = operators have distinct purposes, although they share the common role of assigning values to variables.

= as Assignment

The = operator is primarily used for assignment in Go. It assigns the value on its right-hand side to the variable on its left-hand side. For example:

var x int = 1
y := 2

In the above code, x is explicitly declared as an integer with an initial value of 1, while y is declared using := and automatically infers its type as an integer.

:= as Short Variable Declaration

:= (pronounced "the colon-equals operator") is specifically designed for short variable declarations. This operator combines variable declaration and initialization in a single line. For example:

r := foo()

In this case, r is declared and assigned the result of calling the foo() function. Importantly, := cannot be used to declare variables that have already been declared in the same lexical scope.

Key Differences

The main difference between := and = lies in their usage. := is used for short variable declarations, while = is used for assignments to existing variables or explicitly declared variables. Additionally, := can only appear within functions, while = can be used in any context.

Usage Guidelines

• Use = for assignments to existing variables or explicit variable declarations.
• Use := for short variable declarations, where the variable type is inferred from the expression on the right-hand side.
• Avoid using = in variable declarations, even if it appears to work, as it can lead to unexpected behavior.

Further Resources

• [Variable Declarations in Go](https://go.dev/doc/variables#declarations)
• [Short Variable Declarations](https://go.dev/doc/variables#short_variable_declarations)

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