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Add #[doc(hidden)] to {vga_buffer, serial}::_print functions

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Philipp Oppermann
2018-11-19 10:14:47 +01:00
parent dbfb732325
commit ad7c11c0a3
5 changed files with 13 additions and 2 deletions
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9
blog/content/second-edition/posts/03-vga-text-buffer/index.md
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@@ -605,17 +605,22 @@ macro_rules! println {
($($arg:tt)*) => ($crate::print!("{}\n", format_args!($($arg)*)));
}
#[doc(hidden)]
pub fn _print(args: fmt::Arguments) {
use core::fmt::Write;
WRITER.lock().write_fmt(args).unwrap();
}
```
One thing that we changed from the original `println` definition is that we prefixed the invocations of the `print!` macro with `$crate` too. This ensures that we don't need to have to import the `print!` macro too if we only want to use `println`.
Like in the standard library, we add the `#[macro_export]` attribute to both macros to make them available everywhere in our crate. Note that this places the macros in the root namespace of the crate, so importing them via `use crate::vga_buffer::println` does not work. Instead, we have to do `use crate::println`.
The `_print` function locks our static `WRITER` and calls the `write_fmt` method on it. This method is from the `Write` trait, we need to import that trait. The additional `unwrap()` at the end panics if printing isn't successful. But since we always return `Ok` in `write_str`, that should not happen.
We also add the `#[macro_export]` attribute to both macros to make them available everywhere in our crate. Note that this places the macros in the root namespace of the crate, so importing them via `use crate::vga_buffer::println` does not work. Instead, we have to do `use crate::println`.
Since the macros need to be able to call `_print` from outside of the module, the function needs to be public. However, since we consider this a private implementation detail, we add the [`doc(hidden)` attribute] to hide it from the generated documentation.
One thing that we changed from the original definitions is that we prefixed the invocations of the `print!` macro with `$crate` too. This ensures that we don't need to have to import the `print!` macro too if we only want to use `println`.
[`doc(hidden)` attribute]: https://doc.rust-lang.org/nightly/rustdoc/the-doc-attribute.html#dochidden
### Hello World using `println`
Now we can use `println` in our `_start` function: