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Update beginner/README.md

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Co-authored-by: Lotte Steenbrink <lotte@zombietetris.de>
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Jorge Aparicio 2020-06-23 11:24:41 +00:00 committed by GitHub
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@ -323,7 +323,8 @@ received 5 bytes (LQI=49)
The program broadcasts a radio packet that contains the 5-byte string `Hello` over channel 20 (which has a center frequency of 2450 MHz). The `loopback` program running on the Dongle is listening to all packets sent over channel 20; every time it receives a new packet it reports its length and the Link Quality Indicator (LQI) metric of the transmission over the USB/serial interface. As the name implies the LQI metric indicates how good the connection between the sender and the device is.
*Important note* about `b"Hello"` vs `"Hello"`. The first one is a *byte* string literal value that has type `&[u8; N]`; the second one is a *string* literal value that has type `&str` (`str` is Rust string type). The latter type, `str`, must always be valid UTF-8 data. The former type, `&[u8; N]`, does not place any constraint on its contents. However, the byte string literal syntax (`b".."`) will only accept *non-escaped* characters in the ASCII range (`0x00`..=`0x7F`) so it can *not* contain CJK (Chinese Japanese Korean) characters or emoji for example. String literals (`".."`) can contain any valid UTF-8 content so they can contain CJK characters, emoji, Greek letters, Cyrillic script, etc.
### Character constrains in byte string vs.string literals
You can encode text as `b"Hello"` or as `"Hello"`. `b"Hello"` is a *byte* string literal value that has type `&[u8; N]`; while `"Hello"` is a *string* literal value that has type `&str` (`str` is Rust string type). `str` must always be valid UTF-8 data. The former type, `&[u8; N]`, does not place any constraint on its contents. However, the byte string literal syntax (`b".."`) will only accept *non-escaped* characters in the ASCII range (`0x00`..=`0x7F`) so it can *not* contain CJK (Chinese Japanese Korean) characters or emoji for example. String literals (`".."`) can contain any valid UTF-8 content so they can contain CJK characters, emoji, Greek letters, Cyrillic script, etc.
Now run the `radio-send` program several times with different variations: