modernize-use-structured-binding

Finds places where structured bindings could be used to decompose pairs and suggests replacing them.

This check finds three code patterns and recommends using structured bindings for clearer, more idiomatic C++17 code.

1. Decompose a pair variable by assigning its members to separate variables right after its definition:

auto p = getPair<int, int>();
int x = p.first;
int y = p.second;

into:

auto [x, y] = getPair<int, int>();

2. Use std::tie to decompose a pair into two predefined variables:

int a;
int b;
std::tie(a, b) = getPair<int, int>();

into:

auto [a, b] = getPair<int, int>();

3. Manually decompose a pair by assigning to its members to local variables in a range-based for loop:

for (auto p : vecOfPairs) {
  int x = p.first;
  int y = p.second;
  // ...
}

into:

for (auto [x, y] : vecOfPairs) {
  // use x and y
}

Limitations

The check currently ignores variables defined with attributes or qualifiers except const and & since it’s not very common:

static auto pair = getPair();
static int b = pair.first;
static int c = pair.second;

The check doesn’t handle some situations which could possibly be transferred to structured bindings, for example:

const auto& results = mapping.try_emplace("hello!");
const iterator& it = results.first;
bool succeed = results.second;
// succeed is not changed in the following code

and:

const auto results = mapping.try_emplace("hello!");
if (results.second) {
    handle_inserted(results.first);
}