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Learn Go: Functions
Scope

A function definition creates something called a scope. We’ve referenced scope before in our conditionals exercise about scoped short declarations but it’s important to recognize how scope plays a huge role in functions and programming overall!

Scope is a concept that refers to where the values and functions are defined and where they can be accessed. For instance, when a variable is defined within a function, that variable is only accessible within that function. When we try to access that same variable from a different function, we get an error because we can’t do it. Each function has its own specific scope, take a look at the code:

package main import "fmt" func performAddition() { x := 5 y := 7 fmt.Println("The sum of", x, "and", y, "is", x + y) } func main() { performAddition() fmt.Println("What if", x, "was different?") }

The above code exits with the following error:

./main.go:12:26: undefined: x

The error is raised because the x in main()‘s print statement fmt.Println("What if", x, "was different?") is in a different scope than the defined x inside performAddition(). It’s not possible to directly refer to performAddition()‘s x variable in the scope of main().

There are three different scopes present in this example:

  • The global scope, which contains the function definitions for main() and performAddition().
  • performAddition() has a local scope, which defines x and y.
  • main() has a local scope also. It can access performAddition() because that’s defined on the same scope level as main() but can’t access the internals of performAddition‘s scope (i.e., x or y).

This differentiation of scope keeps the namespace, the available variables and keywords, cleaner as a result. You can only refer to variables or functions defined within a specific namespace.

Instructions

1.

In main.go we have a function that creates the instructions for the start of a game. We’re trying to access the string so that we can print it, but it’s in a different scope from the one our print statement is.

Move the fmt.Println(instructions) statement from the main() function body into startGame()‘s body.

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