Helper classes

Chemfiles contains C++11 implementations of various goodies from more recent versions of the language, or support libraries. Here is a small documentation on how to use these types.


template<class T>
class chemfiles::optional

A class representing optional values. Basic usage example is given here, you can also refer to the documentation for std::optional on cppreference.

For most purposes, one can use an optional<T> value as if it was a pointer T*, with nullopt indicating the absence of a value.

// nullopt is used to indicate the optional data is missing
chemfiles::optional<double> optional = nullopt;

if (optional) {
    // chemfiles::optional is convertible to bool

// setting a value
optional = 78.0;

// extracting the value
double a = *optional;
double b = optional.value();

// specifying a default value to be used if data is missing
double c = optional.value_or(-1);


template<class T>
class chemfiles::span

A span<T> is a view inside a std::vector<T> providing all the operations of a vector except for memory allocation. The idea and implementation comes from the GSL library.

// you should never need to create a span yourself
chemfiles::span<double> span = /* ... */;

// span supports range-based iteration
for (auto a: span) {
    // ...

// but also the usual indexing
for (size_t i=0; i<span.size(); i++) {
    double b = span[i];

// and direct indexing
double b = span[5];
span[6] = 78.3;

// you can also use a span with standard algorithms
auto sum = std::accumulate(span.begin(), span.end(), 0.0);