sl-std: Add utility ascii! macro

This macro is used to construct ascii strings with ease

crates/sl-std/src/ascii/mod.rs

@@ -48,3 +48,30 @@ impl AsciiCharExt for Char {
         }
     }
 }
+
+/// Allows for easy definition of ascii-strings
+///
+/// Since rust does not allow us to define our own string literals, the use of a macro
+/// is necessary. If the provided literal contains non-ascii data then the invocation will
+/// panic at compile-time.
+///
+/// # Example
+/// ```
+/// # #![feature(ascii_char)]
+/// # use sl_std::ascii;
+///
+/// let foo: &ascii::Str = ascii!("foo");
+/// assert_eq!(foo.as_str(), "foo");
+///
+/// ```
+#[macro_export]
+macro_rules! ascii {
+    ($s: expr) => {
+        const {
+            match $s.as_bytes().as_ascii() {
+                Some(ascii) => $crate::ascii::Str::from_ascii_chars(ascii),
+                None => panic!("string literal is not ascii"),
+            }
+        }
+    };
+}