Add illegal task

illegal/README.md

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+# illegal
+
+Используя пакет unsafe, реализуйте "незаконные" функции:
+
+- `SetPrivateField` меняет приватное поле структуры
+- `StringFromBytes` создаёт строку из `[]byte` без доп. аллокаций

illegal/field.go

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+// +build !solution
+
+package illegal
+
+func SetPrivateField(obj interface{}, name string, value interface{}) {
+}

illegal/field_test.go

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+package illegal_test
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"gitlab.com/slon/shad-go/illegal"
+	"gitlab.com/slon/shad-go/illegal/internal"
+)
+
+func TestIllegalField(t *testing.T) {
+	var s internal.Struct
+
+	illegal.SetPrivateField(&s, "a", 10)
+	illegal.SetPrivateField(&s, "b", "foo")
+
+	assert.Equal(t, "10 foo", s.String())
+}

illegal/internal/struct.go

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+// +build !change
+
+package internal
+
+import "fmt"
+
+type Struct struct {
+	a int
+	b string
+}
+
+func (s *Struct) String() string {
+	return fmt.Sprintf("%d %s", s.a, s.b)
+}

illegal/string.go

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+// +build !solution
+
+package illegal
+
+func StringFromBytes(b []byte) string {
+	panic("implement me")
+}

illegal/string_test.go

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+package illegal_test
+
+import (
+	"testing"
+	"unsafe"
+
+	"github.com/stretchr/testify/assert"
+	"gitlab.com/slon/shad-go/illegal"
+)
+
+func TestStringFromBytes(t *testing.T) {
+	b := []byte{'a', 'b', 'c'}
+	s := illegal.StringFromBytes(b)
+
+	assert.Equal(t, "abc", s)
+	assert.Equal(t, **(**uintptr)(unsafe.Pointer(&b)), **(**uintptr)(unsafe.Pointer(&s)))
+}