Learning Go, 2nd Edition

Chapter 4. Blocks, Shadows, and Control Structures

Now that I have covered variables, constants, and built-in types, you are ready to look at programming logic and organization. I’ll start by explaining blocks and how they control when an identifier is available. Then I’ll present Go’s control structures: if, for, and switch. Finally, I will talk about goto and the one situation when you should use it.

Blocks

Go lets you declare variables in lots of places. You can declare them outside of functions, as the parameters to functions, and as local variables within functions.

Note

So far, you’ve written only the main function, but you’ll write functions with parameters in the next chapter.

Each place where a declaration occurs is called a block. Variables, constants, types, and functions declared outside of any functions are placed in the package block. You’ve used import statements in your programs to gain access to printing and math functions (and I will talk about them in detail in Chapter 10). They define names for other packages that are valid for the file that contains the import statement. These names are in the file block. All the variables defined at the top level of a function (including the parameters to a function) are in a block. Within a function, every set of braces ({}) defines another block, and in a bit you will see that the control structures in Go define blocks of their own.

You can access an identifier defined in any outer block from within any inner block. This ...