compare

diff := compare.Diff("A", "B", func(v string) compare.C {
	return compare.C{
		compare.Comparable("v", v),
	}
})

fmt.Println(diff)

Output:

v: "A" != "B"

type S struct {
	I int
}

diff := compare.Diff(&S{1}, &S{2}, func(v *S) compare.C {
	return compare.C{
		compare.ComparablePointer("v", v),
	}
})

fmt.Println(diff)

Output:

v: compare_test.S{I:1} != compare_test.S{I:2}

diff := compare.Diff([]int{1, 2}, []int{3, 4}, func(v []int) compare.C {
	return compare.C{
		compare.ComparableSlice("v", v),
	}
})

fmt.Println(diff)

Output:

v[0]: 1 != 3
v[1]: 2 != 4

t1 := time.Now()
t2 := t1.Add(100 * time.Millisecond)

diff := compare.Diff(t1, t2, func(t time.Time) compare.C {
	return compare.C{
		// Custom comparer to allow maximum 1s diff.
		compare.Func("t", t, func(t1, t2 time.Time) error {
			if t2.Sub(t1).Abs() > time.Second {
				return fmt.Errorf("t1 != t2")
			}
			return nil
		}),
	}
})

if diff == "" {
	fmt.Println("t1 approximately equals t2")
}

Output:

t1 approximately equals t2

type Child struct {
	F1 int
	F2 string
}
type Parent struct {
	Child Child
}

diff := compare.Diff(Parent{Child{1, "child1"}}, Parent{Child{2, "child2"}}, func(parent Parent) compare.C {
	return compare.C{
		compare.Nest("Child", parent.Child, func(child Child) compare.C {
			return compare.C{
				compare.Comparable("F1", child.F1),
				compare.Comparable("F2", child.F2),
			}
		}),
	}
})

fmt.Println(diff)

Output:

Child.F1: 1 != 2
Child.F2: "child1" != "child2"

type S struct {
	F int
}

diff := compare.Diff([]S{{1}, {2}}, []S{{3}, {4}}, func(vs []S) compare.C {
	return compare.C{
		compare.Slice("vs", vs, func(v S) compare.C {
			return compare.C{
				compare.Comparable("F", v.F),
			}
		}),
	}
})

fmt.Println(diff)

Output:

vs[0].F: 1 != 3
vs[1].F: 2 != 4