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#![feature(specialization)]
//! Use debug printlns, without the trait bounds (using specialization to
//! find the right impl anyway).
//!
//! **NOTE**: This uses experimental Rust features and is therefore
//! by itself experimental and unstable, and has all the problems of
//! `feature(specialization)`.
//!
//! For this reason, `unsafe` is required to use this feature unfortunately.
//!
use std::fmt;
use std::any::type_name;
/// Print a message, and then each value's debug representation (if it has one)
///
/// NOTE: This macro has **no** format string, only a message and a list of values.
///
/// # Examples
///
/// ```
/// #[macro_use] extern crate debugit;
///
/// fn process_something<T>(x: T) {
/// unsafe {
/// debugit!("starting with", x);
/// }
/// }
///
/// # fn main() { }
/// ```
#[macro_export]
macro_rules! debugit {
($message:expr, $($value:expr),*) => {{
print!("{} ", $message);
$(
print!("{:?}", $crate::DebugIt(&$value));
)*
println!("");
}};
}
/// This type always implements `Debug`. Uses specialization to use
/// the inner value's Debug (which it should basically always have).
///
/// Otherwise, falls back to print the type name.
///
/// # Examples
///
/// ```
/// use debugit::DebugIt as D;
///
/// fn process_something<T>(x: T) {
/// unsafe {
/// println!("starting with {:?}", D(&x));
/// }
/// }
/// ```
#[derive(Copy, Clone)]
pub struct DebugIt<T> {
value: T
}
/// This type always implements `Debug`. Uses specialization to use
/// the inner value's Debug (which it should basically always have).
///
/// Otherwise, falls back to print the type name.
///
/// # Examples
///
/// ```
/// use debugit::DebugIt as D;
///
/// fn process_something<T>(x: T) {
/// unsafe {
/// println!("starting with {:?}", D(&x));
/// }
/// }
/// ```
pub unsafe fn DebugIt<T>(value: T) -> DebugIt<T> {
DebugIt { value }
}
impl<T> fmt::Debug for DebugIt<T> {
default fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
write!(f, "`{}`", type_name::<T>())
}
}
impl<T> fmt::Debug for DebugIt<T>
where T: fmt::Debug
{
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
self.value.fmt(f)
}
}
#[cfg(test)]
mod tests {
use crate::DebugIt;
#[test]
fn it_works() {
fn debug_no_bound<T>(x: T, s: &str) {
unsafe {
assert_eq!(&format!("{:?}", DebugIt(&x)), s);
}
}
debug_no_bound(1, "1");
debug_no_bound((), "()");
}
}