good good study, day day up!

vendor/gopl.io/ch13/equal/equal.go

@@ -0,0 +1,127 @@
+// Copyright © 2016 Alan A. A. Donovan & Brian W. Kernighan.
+// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
+
+// See page 359.
+
+// Package equal provides a deep equivalence relation for arbitrary values.
+package equal
+
+import (
+	"reflect"
+	"unsafe"
+)
+
+//!+
+func equal(x, y reflect.Value, seen map[comparison]bool) bool {
+	if !x.IsValid() || !y.IsValid() {
+		return x.IsValid() == y.IsValid()
+	}
+	if x.Type() != y.Type() {
+		return false
+	}
+
+	// ...cycle check omitted (shown later)...
+
+	//!-
+	//!+cyclecheck
+	// cycle check
+	if x.CanAddr() && y.CanAddr() {
+		xptr := unsafe.Pointer(x.UnsafeAddr())
+		yptr := unsafe.Pointer(y.UnsafeAddr())
+		if xptr == yptr {
+			return true // identical references
+		}
+		c := comparison{xptr, yptr, x.Type()}
+		if seen[c] {
+			return true // already seen
+		}
+		seen[c] = true
+	}
+	//!-cyclecheck
+	//!+
+	switch x.Kind() {
+	case reflect.Bool:
+		return x.Bool() == y.Bool()
+
+	case reflect.String:
+		return x.String() == y.String()
+
+	// ...numeric cases omitted for brevity...
+
+	//!-
+	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32,
+		reflect.Int64:
+		return x.Int() == y.Int()
+
+	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32,
+		reflect.Uint64, reflect.Uintptr:
+		return x.Uint() == y.Uint()
+
+	case reflect.Float32, reflect.Float64:
+		return x.Float() == y.Float()
+
+	case reflect.Complex64, reflect.Complex128:
+		return x.Complex() == y.Complex()
+	//!+
+	case reflect.Chan, reflect.UnsafePointer, reflect.Func:
+		return x.Pointer() == y.Pointer()
+
+	case reflect.Ptr, reflect.Interface:
+		return equal(x.Elem(), y.Elem(), seen)
+
+	case reflect.Array, reflect.Slice:
+		if x.Len() != y.Len() {
+			return false
+		}
+		for i := 0; i < x.Len(); i++ {
+			if !equal(x.Index(i), y.Index(i), seen) {
+				return false
+			}
+		}
+		return true
+
+	// ...struct and map cases omitted for brevity...
+	//!-
+	case reflect.Struct:
+		for i, n := 0, x.NumField(); i < n; i++ {
+			if !equal(x.Field(i), y.Field(i), seen) {
+				return false
+			}
+		}
+		return true
+
+	case reflect.Map:
+		if x.Len() != y.Len() {
+			return false
+		}
+		for _, k := range x.MapKeys() {
+			if !equal(x.MapIndex(k), y.MapIndex(k), seen) {
+				return false
+			}
+		}
+		return true
+		//!+
+	}
+	panic("unreachable")
+}
+
+//!-
+
+//!+comparison
+// Equal reports whether x and y are deeply equal.
+//!-comparison
+//
+// Map keys are always compared with ==, not deeply.
+// (This matters for keys containing pointers or interfaces.)
+//!+comparison
+func Equal(x, y interface{}) bool {
+	seen := make(map[comparison]bool)
+	return equal(reflect.ValueOf(x), reflect.ValueOf(y), seen)
+}
+
+type comparison struct {
+	x, y unsafe.Pointer
+	t    reflect.Type
+}
+
+//!-comparison

vendor/gopl.io/ch13/equal/equal_test.go

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+// Copyright © 2016 Alan A. A. Donovan & Brian W. Kernighan.
+// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
+
+package equal
+
+import (
+	"bytes"
+	"fmt"
+	"testing"
+)
+
+func TestEqual(t *testing.T) {
+	one, oneAgain, two := 1, 1, 2
+
+	type CyclePtr *CyclePtr
+	var cyclePtr1, cyclePtr2 CyclePtr
+	cyclePtr1 = &cyclePtr1
+	cyclePtr2 = &cyclePtr2
+
+	type CycleSlice []CycleSlice
+	var cycleSlice CycleSlice
+	cycleSlice = append(cycleSlice, cycleSlice)
+
+	ch1, ch2 := make(chan int), make(chan int)
+	var ch1ro <-chan int = ch1
+
+	type mystring string
+
+	var iface1, iface1Again, iface2 interface{} = &one, &oneAgain, &two
+
+	for _, test := range []struct {
+		x, y interface{}
+		want bool
+	}{
+		// basic types
+		{1, 1, true},
+		{1, 2, false},   // different values
+		{1, 1.0, false}, // different types
+		{"foo", "foo", true},
+		{"foo", "bar", false},
+		{mystring("foo"), "foo", false}, // different types
+		// slices
+		{[]string{"foo"}, []string{"foo"}, true},
+		{[]string{"foo"}, []string{"bar"}, false},
+		{[]string{}, []string(nil), true},
+		// slice cycles
+		{cycleSlice, cycleSlice, true},
+		// maps
+		{
+			map[string][]int{"foo": {1, 2, 3}},
+			map[string][]int{"foo": {1, 2, 3}},
+			true,
+		},
+		{
+			map[string][]int{"foo": {1, 2, 3}},
+			map[string][]int{"foo": {1, 2, 3, 4}},
+			false,
+		},
+		{
+			map[string][]int{},
+			map[string][]int(nil),
+			true,
+		},
+		// pointers
+		{&one, &one, true},
+		{&one, &two, false},
+		{&one, &oneAgain, true},
+		{new(bytes.Buffer), new(bytes.Buffer), true},
+		// pointer cycles
+		{cyclePtr1, cyclePtr1, true},
+		{cyclePtr2, cyclePtr2, true},
+		{cyclePtr1, cyclePtr2, true}, // they're deeply equal
+		// functions
+		{(func())(nil), (func())(nil), true},
+		{(func())(nil), func() {}, false},
+		{func() {}, func() {}, false},
+		// arrays
+		{[...]int{1, 2, 3}, [...]int{1, 2, 3}, true},
+		{[...]int{1, 2, 3}, [...]int{1, 2, 4}, false},
+		// channels
+		{ch1, ch1, true},
+		{ch1, ch2, false},
+		{ch1ro, ch1, false}, // NOTE: not equal
+		// interfaces
+		{&iface1, &iface1, true},
+		{&iface1, &iface2, false},
+		{&iface1Again, &iface1, true},
+	} {
+		if Equal(test.x, test.y) != test.want {
+			t.Errorf("Equal(%v, %v) = %t",
+				test.x, test.y, !test.want)
+		}
+	}
+}
+
+func Example_equal() {
+	//!+
+	fmt.Println(Equal([]int{1, 2, 3}, []int{1, 2, 3}))        // "true"
+	fmt.Println(Equal([]string{"foo"}, []string{"bar"}))      // "false"
+	fmt.Println(Equal([]string(nil), []string{}))             // "true"
+	fmt.Println(Equal(map[string]int(nil), map[string]int{})) // "true"
+	//!-
+
+	// Output:
+	// true
+	// false
+	// true
+	// true
+}
+
+func Example_equalCycle() {
+	//!+cycle
+	// Circular linked lists a -> b -> a and c -> c.
+	type link struct {
+		value string
+		tail  *link
+	}
+	a, b, c := &link{value: "a"}, &link{value: "b"}, &link{value: "c"}
+	a.tail, b.tail, c.tail = b, a, c
+	fmt.Println(Equal(a, a)) // "true"
+	fmt.Println(Equal(b, b)) // "true"
+	fmt.Println(Equal(c, c)) // "true"
+	fmt.Println(Equal(a, b)) // "false"
+	fmt.Println(Equal(a, c)) // "false"
+	//!-cycle
+
+	// Output:
+	// true
+	// true
+	// true
+	// false
+	// false
+}