Where is erase_if?

Question

I\'ve got a container and would like to erase elements based on a predicate. erase_if sounds familiar, but I can\'t find it in C++. What\'s the name and where i

Answer 1

MSVC does not yet implement C++20's std::erase_if from P1209R0 so, as a workaround, you can just copy the implementation for specific container from that paper somewhere to your code. GCC 9.1 and Clang 9.0 already have it.

namespace std {

// for std::string
template 
void erase_if(basic_string& c, Predicate pred) {
    c.erase(remove_if(c.begin(), c.end(), pred), c.end());
}

// for std::deque
template 
void erase_if(deque& c, Predicate pred) {
    c.erase(remove_if(c.begin(), c.end(), pred), c.end());
}

// for std::vector
template 
void erase_if(vector& c, Predicate pred) {
    c.erase(remove_if(c.begin(), c.end(), pred), c.end());
}

// for std::list
template 
void erase_if(list& c, Predicate pred) {
    c.remove_if(pred);
}

// for std::forward_list
template 
void erase_if(forward_list& c, Predicate pred) {
    c.remove_if(pred);
}

// for std::map
template 
void erase_if(map& c, Predicate pred) {
    for (auto i = c.begin(), last = c.end(); i != last; )
        if (pred(*i))
            i = c.erase(i);
        else
            ++i;
}

// for std::multimap
template 
void erase_if(multimap& c, Predicate pred) {
    for (auto i = c.begin(), last = c.end(); i != last; )
        if (pred(*i))
            i = c.erase(i);
        else
            ++i;
}

// for std::set
template 
void erase_if(set& c, Predicate pred) {
    for (auto i = c.begin(), last = c.end(); i != last; )
        if (pred(*i))
            i = c.erase(i);
        else
            ++i;
}

// for std::multiset
template 
void erase_if(multiset& c, Predicate pred) {
    for (auto i = c.begin(), last = c.end(); i != last; )
        if (pred(*i))
            i = c.erase(i);
        else
            ++i;
}

// for std::unordered_map
template 
void erase_if(unordered_map& c, Predicate pred) {
    for (auto i = c.begin(), last = c.end(); i != last; )
        if (pred(*i))
            i = c.erase(i);
        else
            ++i;
}

// for std::unordered_multimap
template 
void erase_if(unordered_multimap& c, Predicate pred) {
    for (auto i = c.begin(), last = c.end(); i != last; )
        if (pred(*i))
            i = c.erase(i);
        else
            ++i;
}

// for std::unordered_set
template 
void erase_if(unordered_set& c, Predicate pred) {
    for (auto i = c.begin(), last = c.end(); i != last; )
        if (pred(*i))
            i = c.erase(i);
        else
            ++i;
}

// for std::unordered_multiset
template 
void erase_if(unordered_multiset& c, Predicate pred) {
    for (auto i = c.begin(), last = c.end(); i != last; )
        if (pred(*i))
            i = c.erase(i);
        else
            ++i;
}

} // namespace std