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# Comments
Any program requires comments, and Rust supports
a few different varieties:
* *Regular comments* which are ignored by the compiler:
* `// Line comments which go to the end of the line.`
* `/* Block comments which go to the closing delimiter. */`
* *Doc comments* which are parsed into HTML library [documentation][docs]:
* `/// Generate library docs for the following item.`
* `//! Generate library docs for the enclosing item.`
```rust,editable
fn main() {
// This is an example of a line comment.
// There are two slashes at the beginning of the line.
// And nothing written inside these will be read by the compiler.
// println!("Hello, world!");
// Run it. See? Now try deleting the two slashes, and run it again.
/*
* This is another type of comment, a block comment. In general,
* line comments are the recommended comment style. But block comments
* are extremely useful for temporarily disabling chunks of code.
* /* Block comments can be /* nested, */ */ so it takes only a few
* keystrokes to comment out everything in this main() function.
* /*/*/* Try it yourself! */*/*/
*/
/*
Note: The previous column of `*` was entirely for style. There's
no actual need for it.
*/
// You can manipulate expressions more easily with block comments
// than with line comments. Try deleting the comment delimiters
// to change the result:
let x = 5 + /* 90 + */ 5;
println!("Is `x` 10 or 100? x = {}", x);
}
```
### See also:
[Library documentation][docs]
[docs]: ../meta/doc.md
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