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fix code style

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Thibault Kruse 2016-09-05 22:17:03 +09:00
parent 603a1b4286
commit 13419aa5dd
1 changed files with 55 additions and 44 deletions
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CppCoreGuidelines.md
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@ -7368,7 +7368,7 @@ Wrap a `union` in a class together with a type field.
The soon-to-be-standard `variant` type (to be found in `<variant>`) does that for you:
variant<int,double> v;
variant<int, double> v;
v = 123; // v holds an int
int x = get<int>(v);
v = 123.456; // v holds a double
@ -7420,19 +7420,19 @@ Saving programmers from having to write such code is one reason for including `v
int Value::number() const
{
if (type!=Tag::number) throw Bad_entry{};
if (type != Tag::number) throw Bad_entry{};
return i;
}
string Value::text() const
{
if (type!=Tag::text) throw Bad_entry{};
if (type != Tag::text) throw Bad_entry{};
return s;
}
void Value::set_number(int n)
{
if (type==Tag::text) {
if (type == Tag::text) {
s.~string(); // explicitly destroy string
type = Tag::number;
}
@ -7441,7 +7441,7 @@ Saving programmers from having to write such code is one reason for including `v
void Value::set_text(const string& ss)
{
if (type==Tag::text)
if (type == Tag::text)
s = ss;
else {
new(&s) string{ss}; // placement new: explicitly construct string
@ -7451,12 +7451,12 @@ Saving programmers from having to write such code is one reason for including `v
Value& Value::operator=(const Value& e) // necessary because of the string variant
{
if (type==Tag::text && e.type==Tag::text) {
if (type == Tag::text && e.type == Tag::text) {
s = e.s; // usual string assignment
return *this;
}
if (type==Tag::text) s.~string(); // explicit destroy
if (type == Tag::text) s.~string(); // explicit destroy
switch (e.type) {
case Tag::number:
@ -7472,7 +7472,7 @@ Saving programmers from having to write such code is one reason for including `v
Value::~Value()
{
if (type==Tag::text) s.~string(); // explicit destroy
if (type == Tag::text) s.~string(); // explicit destroy
}
##### Enforcement
@ -9168,7 +9168,7 @@ Reuse of a member name as a local variable can also be a problem:
void S::f(int x)
{
m=7; // assign to member
m = 7; // assign to member
if (x) {
int m = 9;
// ...
@ -9487,7 +9487,9 @@ For containers, there is a tradition for using `{...}` for a list of elements an
Initialization of a variable declared using `auto` with a single value, e.g., `{v}`, had surprising results until recently:
auto x1 {7}; // x1 is an int with the value 7
auto x2 = {7}; // x2 is an initializer_list<int> with an element 7 (this will will change to "element 7" in C++17)
// x2 is an initializer_list<int> with an element 7
// (this will will change to "element 7" in C++17)
auto x2 = {7};
auto x11 {7, 8}; // error: two initializers
auto x22 = {7, 8}; // x2 is an initializer_list<int> with elements 7 and 8
@ -10511,7 +10513,7 @@ Consider keeping previously computed results around for a costly operation:
class Cache { // some type implementing a cache for an int->int operation
public:
pair<bool,int> find(int x) const; // is there a value for x?
pair<bool, int> find(int x) const; // is there a value for x?
void set(int x, int v); // make y the value for x
// ...
private:
@ -10520,12 +10522,12 @@ Consider keeping previously computed results around for a costly operation:
class X {
public:
int get_val(int x)
int get_val(int x)
{
auto p = cache.find(x);
if (p.first) return p.second;
int val = compute(x);
cache.set(x,val); // insert value for x
cache.set(x, val); // insert value for x
return val;
}
// ...
@ -10541,10 +10543,10 @@ To do this we still need to mutate `cache`, so people sometimes resort to a `con
int get_val(int x) const
{
auto p = cache.find(x);
if (p.first) return p.second;
int val = compute(x);
const_cast<Cache&>(cache).set(x,val); // ugly
return val;
if (p.first) return p.second;
int val = compute(x);
const_cast<Cache&>(cache).set(x, val); // ugly
return val;
}
// ...
private:
@ -10561,7 +10563,7 @@ State that `cache` is mutable even for a `const` object:
auto p = cache.find(x);
if (p.first) return p.second;
int val = compute(x);
cache.set(x,val);
cache.set(x, val);
return val;
}
// ...
@ -10856,7 +10858,7 @@ Avoid wrong results.
unsigned int y = 7;
cout << x - y << '\n'; // unsigned result, possibly 4294967286
cout << x + y << '\n'; // unsiged result: 4
cout << x + y << '\n'; // unsigned result: 4
cout << x * y << '\n'; // unsigned result, possibly 4294967275
It is harder to spot the problem in more realistic examples.
@ -10939,12 +10941,15 @@ The build-in array uses signed types for subscripts.
This makes surprises (and bugs) inevitable.
int a[10];
for (int i=0; i<10; ++i) a[i]=i;
for (int i=0; i < 10; ++i) a[i]=i;
vector<int> v(10);
for (int i=0; v.size()<10; ++i) v[i]=i; // compares signed to unsigned; some compilers warn
// compares signed to unsigned; some compilers warn
for (int i=0; v.size() < 10; ++i) v[i]=i;
int a2[-2]; // error: negative size
vector<int> v2(-2); // OK, but the number of ints (4294967294) is so large that we should get an exception
// OK, but the number of ints (4294967294) is so large that we should get an exception
vector<int> v2(-2);
##### Enforcement
@ -11190,7 +11195,7 @@ Because a design that ignore the possibility of later improvement is hard to cha
From the C (and C++) standard:
void qsort (void* base, size_t num, size_t size, int (*compar)(const void*,const void*));
void qsort (void* base, size_t num, size_t size, int (*compar)(const void*, const void*));
When did you even want to sort memory?
Really, we sort sequences of elements, typically stored in containers.
@ -11200,7 +11205,10 @@ This implies added work for the programmer, is error prone, and deprives the com
double data[100];
// ... fill a ...
qsort(data,100,sizeof(double),compare_doubles); // 100 chunks of memory of sizeof(double) starting at address data using the order defined by compare_doubles
// 100 chunks of memory of sizeof(double) starting at
// address data using the order defined by compare_doubles
qsort(data, 100, sizeof(double), compare_doubles);
From the point of view of interface design is that `qsort` throws away useful information.
@ -11209,13 +11217,15 @@ We can do better (in C++98)
template<typename Iter>
void sort(Iter b, Iter e); // sort [b:e)
sort(data,data+100);
sort(data, data + 100);
Here, we use the compiler's knowledge about the size of the array, the type of elements, and how to compare `double`s.
With C++11 plus [concepts](#???), we can do better still
void sort(Sortable& c); // Sortable specifies that c must be a random-access sequence of elements comparable with <
// Sortable specifies that c must be a
// random-access sequence of elements comparable with <
void sort(Sortable& c);
sort(c);
@ -11224,17 +11234,18 @@ In this, the `sort` interfaces shown here still have a weakness:
They implicitly rely on the element type having less-than (`<`) defined.
To complete the interface, we need a second version that accepts a comparison criteria:
void sort(Sortable& c, Predicate<Value_type<Sortable>> p); // compare elements of c using p
// compare elements of c using p
void sort(Sortable& c, Predicate<Value_type<Sortable>> p);
The standard-library specification of `sort` offers those two versions,
but the semantics is expressed in English rather than code using concepts.
##### Note
##### Note
Premature optimization is said to be [the root of all evil](#Rper-Knuth), but that's not a reason to despise performance.
It is never premature to consider what makes a design amenable to improvement, and improved performance is a commonly desired improvement.
Aim to build a set of habits that by default results in efficient, maintainable, and optimizable code.
In particular, when you write a function that is not a one-off implementation detail, consider
In particular, when you write a function that is not a one-off implementation detail, consider
* Information passing:
Prefer clean [interfaces](#S-interfaces) carrying sufficient information for later improvement of implementation.
@ -11267,7 +11278,7 @@ Don't let bad designs "bleed into" your code.
Consider:
template <class ForwardIterator, class T>
bool binary_search (ForwardIterator first, ForwardIterator last, const T& val);
bool binary_search(ForwardIterator first, ForwardIterator last, const T& val);
`binary_search(begin(c),end(c),7)` will tell you whether `7` is in `c` or not.
However, it will not tell you where that `7` is or whether there are more than one `7`.
@ -11280,16 +11291,16 @@ needed information back to the caller. Therefore, the standard library also offe
`lower_bound` returns an iterator to the first match if any, otherwise `last`.
However, `lower_bound` still doesn't return enough information for all uses, so the standard library also offers
However, `lower_bound` still doesn't return enough information for all uses, so the standard library also offers
template <class ForwardIterator, class T>
pair<ForwardIterator,ForwardIterator>
equal_range (ForwardIterator first, ForwardIterator last, const T& val);
pair<ForwardIterator, ForwardIterator>
equal_range(ForwardIterator first, ForwardIterator last, const T& val);
`equal_range` returns a `pair` of iterators specifying the first and one beyond last match.
auto r = equal_range(begin(c),end(c),7);
for (auto p = r.first(); p!=r.second(), ++p)
auto r = equal_range(begin(c), end(c),7);
for (auto p = r.first(); p != r.second(), ++p)
cout << *p << '\n';
Obviously, these three interfaces are implemented by the same basic code.
@ -16546,9 +16557,9 @@ In particular, the single-return rule makes it harder to concentrate error check
// requires Number<T>
string sign(T x)
{
if (x<0)
if (x < 0)
return "negative";
else if (x>0)
else if (x > 0)
return "positive";
return "zero";
}
@ -16560,12 +16571,12 @@ to use a single return only we would have to do something like
string sign(T x) // bad
{
string res;
if (x<0)
if (x < 0)
res = "negative";
else if (x>0)
else if (x > 0)
res = "positive";
else
res ="zero";
res = "zero";
return res;
}
@ -16577,7 +16588,7 @@ Of course many simple functions will naturally have just one `return` because of
int index(const char* p)
{
if (p==nullptr) return -1; // error indicator: alternatively `throw nullptr_error{}`
if (p == nullptr) return -1; // error indicator: alternatively "throw nullptr_error{}"
// ... do a lookup to find the index for p
return i;
}
@ -16587,7 +16598,7 @@ If we applied the rule, we'd get something like
int index2(const char* p)
{
int i;
if (p==nullptr)
if (p == nullptr)
i = -1; // error indicator
else {
// ... do a lookup to find the index for p
@ -16715,9 +16726,9 @@ This technique is a pre-exception technique for RAII-like resource and error han
void do_something(int n)
{
if (n<100) goto exit;
if (n < 100) goto exit;
// ...
int* p = (int*)malloc(n);
int* p = (int*) malloc(n);
// ...
if (some_ error) goto_exit;
// ...