Implement print_char

[JonasFocke01]

Hello,

this PR addresses issue #4 by implementing a print_chars() function.
This uses your techniques. Please let me know, if i did something wrong.
I have tested this on multiple display-pico combinations with great success.
As the display is sort of limited in its capabilities, some letters look a bit wrong, but i tried my best to follow this picture (with some assumptions involved).
The function increases the footprint of this library, by adding a mapping-helper-function that stores all A-z chars if used.

Cheers!

[igelbox]

Well, I kinda intentionally avoided adding any alphabets here coz the device doesn't natively support letters so displaying any is an approximation/imagination.
Also, I do believe it's not that complicated to implement any additional methods like print_chars as part of additional trait for the pub struct TM1637. So I believe (but not sure though) you could implement your own library that would extend this one with the additional trait with the print_chars method.

[igelbox]

I do believe it's not that complicated

It definitely is =)

diff --git a/examples/main.rs b/examples/main.rs
index 94e0064..bb01ca8 100644
--- a/examples/main.rs
+++ b/examples/main.rs
@@ -5,8 +5,10 @@
 extern crate panic_halt;
 
 extern crate stm32f103xx_hal as hal;
+extern crate embedded_hal as ehal;
 
 use hal::delay::Delay;
+use ehal::digital::v2::{InputPin, OutputPin};
 use hal::prelude::*;
 use hal::stm32f103xx::Peripherals;
 use embedded_hal::blocking::delay::DelayUs;
@@ -14,13 +16,37 @@ use embedded_hal::blocking::delay::DelayUs;
 use cortex_m_rt::entry;
 
 extern crate tm1637;
-use tm1637::{ TM1637 };
+use tm1637::{ TM1637, Error };
 
 struct NoDelay {}
 impl DelayUs<u16> for NoDelay {
     fn delay_us(&mut self, us: u16) {}
 }
 
+trait PrintChars<E> {
+    fn print_chars(&mut self, address: u8, chars: &[char])->Result<(), Error<E>>;
+}
+
+// I wish Rust has some way to extend generic traits without explicit bounds re-definition
+// so all the types may be infered from those are used in TM1637
+impl<'a, CLK, DIO, D, E> PrintChars<E> for TM1637<'a, CLK, DIO, D>
+where
+    CLK: OutputPin<Error = E>,
+    DIO: InputPin<Error = E> + OutputPin<Error = E>,
+    D: DelayUs<u16>,
+{
+    fn print_chars(&mut self, address: u8, chars: &[char])->Result<(), Error<E>> {
+        self.print_raw_iter(address, chars.iter().map(|b| char_to_raw(*b)))
+    }
+}
+
+fn char_to_raw(c: char) -> u8 {
+    match c {
+        'a' | 'A' => 0x77,
+        _ => 0x00,
+    }
+}
+
 #[entry]
 fn main() -> ! {
     let dp = Peripherals::take().unwrap();
@@ -49,6 +75,8 @@ fn main() -> ! {
             tm.print_raw(3, &[i]);
 
             tm.set_brightness(i >> 5);
+
+            tm.print_chars(0, &['A', 'a']);
         }
     }
 }

it compiles but I have no device to check how it works.
So it seems the approach with a separate library is kinda (generic-type mess hurts) viable.

[igelbox]

It would be great if Rust allow write just:

impl for TM1637 /*please, do it for all TM1637 specialisations*/ {
    fn print_chars(&mut self, address: u8, chars: &[char]) /*please, infer the result type for me =)*/ {
        self.print_raw_iter(address, chars.iter().map(|b| char_to_raw(*b)))
    }
}

just to decouple this function implementation from the library implementation details.
But I have no experience/idea to make it work this way.

[JonasFocke01]

But that would require the user to write this trait out with all its generic types.
We could hide this print_chars() behind a feature flag and do it for them, so we could sidestep a whole trait.
And/or create an example, how one could utilize the print_raw_iter() function, to print custom chars, so he would not have to figure that out.

I introduced a chars feature, that is NOT enabled by default.
Your opinions?

[JonasFocke01]

I also think about adding a hex feature to be in line with my prev. comment.