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Diffstat (limited to 'doc/go_tutorial.txt')
| -rw-r--r-- | doc/go_tutorial.txt | 48 |
1 files changed, 30 insertions, 18 deletions
diff --git a/doc/go_tutorial.txt b/doc/go_tutorial.txt index 7c0ffac80..93344257f 100644 --- a/doc/go_tutorial.txt +++ b/doc/go_tutorial.txt @@ -47,6 +47,33 @@ The comment convention is the same as in C++: Later we'll have much more to say about printing. +Semicolons +---- + +You might have noticed that our program has no semicolons. In Go +code, the only place you typically see semicolons is separating the +clauses of "for" loops and the like; they are not necessary after +every statement. + +In fact, what happens is that the formal language uses semicolons, +much as in C or Java, but they are inserted automatically +at the end of every line that looks like the end of a statement. You +don't need to type them yourself. + +For details about how this is done you can see the language +specification, but in practice all you need to know is that you +never need to put a semicolon at the end of a line. (You can put +them in if you want to write multiple statements per line.) As an +extra help, you can also leave out a semicolon immediately before +a closing brace. + +This approach makes for clean-looking, semicolon-free code. The +one surprise is that it's important to put the opening +brace of a construct such as an "if" statement on the same line as +the "if"; if you don't, there are situations that may not compile +or may give the wrong result. The language forces the brace style +to some extent. + Compiling ---- @@ -84,27 +111,12 @@ This program is small but it's doing a number of new things. In the last exampl we saw "func" introduce a function. The keywords "var", "const", and "type" (not used yet) also introduce declarations, as does "import". Notice that we can group declarations of the same sort into -parenthesized, semicolon-separated lists if we want, as on lines 7-10 and 14-17. +parenthesized lists, one item per line, as on lines 7-10 and 14-17. But it's not necessary to do so; we could have said const Space = " " const Newline = "\n" -Semicolons aren't needed here; in fact, semicolons are unnecessary after any -top-level declaration, although they are needed as separators <i>within</i> -a parenthesized list of declarations. - -You can use semicolons just the way you would in C, C++, or Java, but if you -prefer you can also leave them out in many cases. They <i>separate</i> statements -rather than terminate them, so they aren't needed (but are still OK) at the end of the last -statement in a block. -They're also optional after braces, as in C. -Have a look at the source to "echo". -The only necessary semicolons in that program are on lines 8, 15, and 21 -and of course between the elements of the "for" loop on line 22. -The ones on line 9, 16, 26, and 31 are optional but are there because a semicolon -on the end of a list of statements makes it easier to edit the list later. - This program imports the ""os"" package to access its "Stdout" variable, of type "*os.File". The "import" statement is actually a declaration: in its general form, as used in our ``hello world'' program, @@ -634,7 +646,7 @@ prints In fact, if you're lazy the format "%v" will print, in a simple appropriate style, any value, even an array or structure. The output of ---PROG progs/print.go 'NR==14' 'NR==17' +--PROG progs/print.go 'NR==14' 'NR==20' is @@ -647,7 +659,7 @@ of "%v" while "Println" inserts spaces between arguments and adds a newline. The output of each of these two lines is identical to that of the "Printf" call above. ---PROG progs/print.go 'NR==18' 'NR==19' +--PROG progs/print.go 'NR==21' 'NR==22' If you have your own type you'd like "Printf" or "Print" to format, just give it a "String()" method that returns a string. The print |