ptth/crates/always_equal/src/lib.rs

pub mod test {
	#[derive (Debug)]
	pub struct AlwaysEqual <T> {
		inner: Option <T>,
	}

	impl <T> AlwaysEqual <T> {
		pub fn into_inner (self) -> T {
			match self.inner {
				Some (x) => x,
				None => unreachable! (),
			}
		}
		
		pub fn testing_blank () -> Self {
			Self {
				inner: None,
			}
		}
	}

	impl <T: Default> Default for AlwaysEqual <T> {
		fn default () -> Self {
			Self::from (T::default ())
		}
	}

	impl <T> From <T> for AlwaysEqual <T> {
		fn from (inner: T) -> Self {
			Self {
				inner: Some (inner),
			}
		}
	}

	impl <T> PartialEq for AlwaysEqual <T> {
		fn eq (&self, other: &Self) -> bool {
			self.inner.is_none () || other.inner.is_none ()
		}
	}
}

pub mod prod {
	use std::fmt;
	
	pub struct AlwaysEqual <T> {
		inner: T,
	}
	
	impl <T: fmt::Debug> fmt::Debug for AlwaysEqual <T> {
		fn fmt (&self, f: &mut fmt::Formatter) -> fmt::Result {
			self.inner.fmt (f)
		}
	}
	
	impl <T: fmt::Display> fmt::Display for AlwaysEqual <T> {
		fn fmt (&self, f: &mut fmt::Formatter) -> fmt::Result {
			self.inner.fmt (f)
		}
	}
	
	impl <T> AlwaysEqual <T> {
		pub fn into_inner (self) -> T {
			self.inner
		}
	}
	
	impl <T> From <T> for AlwaysEqual <T> {
		fn from (inner: T) -> Self {
			Self {
				inner,
			}
		}
	}
	
	impl <T> PartialEq for AlwaysEqual <T> {
		fn eq (&self, _other: &Self) -> bool {
			false
		}
	}
}

#[cfg (test)]
mod tests {
	use std::fs::File;
	
	use super::test::*;
	
	// Can't impl Clone or PartialEq because of the File
	type CantCompare = Option <File>;

	#[derive (Debug, Default, PartialEq)]
	struct MyStruct
	{
		file: AlwaysEqual <CantCompare>,
		name: &'static str,
	}
	
	#[test]
	fn test_1 () {
		let concrete_1 = MyStruct {
			file: None.into (),
			name: "my_struct",
		};
		let concrete_2 = MyStruct {
			file: None.into (),
			name: "my_struct",
		};
		let concrete_bad = MyStruct {
			file: None.into (),
			name: "not_my_struct",
		};
		
		assert_ne! (concrete_1, concrete_2);
		assert_ne! (concrete_2, concrete_bad);
		assert_ne! (concrete_bad, concrete_1);
		
		let dummy_1 = MyStruct {
			file: AlwaysEqual::testing_blank (),
			name: "my_struct",
		};
		let dummy_2 = MyStruct {
			file: AlwaysEqual::testing_blank (),
			name: "my_struct",
		};
		let dummy_bad = MyStruct {
			file: AlwaysEqual::testing_blank (),
			name: "not_my_struct",
		};
		
		assert_eq! (dummy_1, dummy_2);
		assert_ne! (dummy_2, dummy_bad);
		assert_ne! (dummy_bad, dummy_1);
		
		assert_eq! (concrete_1, dummy_1);
		assert_eq! (concrete_bad, dummy_bad);
	}
	
	#[test]
	fn test_2 () {
		let v1 = Vec::<AlwaysEqual <File>>::new ();
		let v2 = Vec::<AlwaysEqual <File>>::new ();
		
		assert_eq! (v1, v2);
	}
}