C++20 introduces the member function contains on associative containers to check if an equivalent to a specific key already exists in
the container.
Calling this function can replace previous ways to check if a key is present in a container:
- call
find() and check that its result is not the end of the container. This was quite verbose.
- call
count(). This did not clearly express the intent and was not optimal in terms of performance for containers that allow a key
to be present multiple times.
This rule raises an issue when contains could be used to simplify the code.
Noncompliant code example
void f1(std::set<int> &s) {
if (s.find(1) == s.end()) { // Noncompliant
doSomething();
}
}
void f2(std::unordered_map<std::string, int> &m) {
if (m.count("key") != 0) { // Noncompliant
doSomething();
}
}
Compliant solution
void f1(std::set<int> &s) {
if (!s.contains(1)) { // Compliant
doSomething();
}
}
void f2(std::unordered_map<std::string, int> &m) {
if (m.contains("key")) { // Compliant
doSomething();
}
}
