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>();

  1. 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);
}