visit_diff

Function debug_diff

Source 
pub fn debug_diff<T>(a: T, b: T) -> impl Debug
where
    T: Diff,
Expand description

Given two values that can be diffed, returns an object that will describe their differences when formatted using Debug.

The result can be used anywhere you’d normally format something with Debug, such as calls to println!:

use visit_diff::{Diff, debug_diff};

#[derive(Diff, Debug)]
struct ExampleStruct {
    name: &'static str,
    age: usize,
}

let left = ExampleStruct { name: "Bob", age: 4 };
let right = ExampleStruct { name: "Rototron 3k", age: 5 };

println!("Compact: {:?}", debug_diff(&left, &right));
println!("Pretty: {:#?}", debug_diff(&left, &right));

This prints:

Compact: DIFF { L: ExampleStruct { name: "Bob", age: 4 }, R: ExampleStruct { name: "Rototron 3k", age: 5 } }
Pretty: DIFF {
    L: ExampleStruct {
        name: "Bob",
        age: 4
    },
    R: ExampleStruct {
        name: "Rototron 3k",
        age: 5
    }
}

This is showing the DIFF at the top level, because all fields of the structs are different. If only a single field is different, a more precise diff happens:

let left = ExampleStruct { name: "Bob", age: 4 };
let right = ExampleStruct { name: "Bob", age: 5 };

println!("Compact: {:?}", debug_diff(&left, &right));
println!("Pretty: {:#?}", debug_diff(&left, &right));

This now prints:

Compact: ExampleStruct { name: "Bob", age: DIFF { L: 4, R: 5 } }
Pretty: ExampleStruct {
    name: "Bob",
    age: DIFF {
        L: 4,
        R: 5
    }
}

If you’re curious: debug_diff uses all_different to decide to pull a DIFF indicator up one level of structure.

Examples found in repository?
examples/basic.rs (line 66)
34fn main() {
35    let a = Newtype(Top {
36        child1: Child1 {
37            name: "Sprocket",
38            size: 12,
39        },
40        others: vec![
41            Other::Prince,
42            Other::Bob {
43                last_name: "Roberts",
44            },
45        ],
46    });
47
48    let b = Newtype(Top {
49        // Note: both name and size are different.
50        child1: Child1 {
51            name: "Ralph",
52            size: usize::max_value(),
53        },
54        others: vec![
55            Other::Prince,
56            Other::Bob {
57                last_name: "Roberts",
58            },
59            // added
60            Other::Bob {
61                last_name: "Bobberson",
62            },
63        ],
64    });
65
66    println!("{:#?}", debug_diff(a, b));
67}