How to use preferences

Preferences

Opens the preferences file of the application. The location of the preferences file is operating system depended. On windows this file is located in: \USERPROFILE%\AppData\Local\<vendor>\<application name>\preferences.json

auto preferences = hi::preferences(hi::URL::urlFromApplicationPreferencesFile());

Observer values are linked to values in the preferences located using a json-path. In the example below the json-path is "bar.foo" which results in the preferences file as {"bar": {"foo": 1}}:

hi::observer<int> foo;
preferences.add("bar.foo", foo);
 
// Everytime the program loads the value in the preference file is incremented.
++foo;

Complex types

The example above will work with observers with types that can be natively stored in a json file: integers, floating point, booleans, strings, vectors and maps.

For more complex types, you will need to add a template specialization for hi::pickle. This specialization adds an encoder and decoder between the complex type and a hi::datum. The hi::preferences knows how to read and write a json file using hi::datum values.

The example below shows how to specialize hi::pickle for the complex foo_type type:

struct foo_type {
    int one;
    int two;
 
    friend bool operator==(foo_type const &, foo_type const &) = default;
};
 
template<>
struct hi::pickle<foo_type> {
    [[nodiscard]] datum encode(foo_type const& x) const noexcept {
        return datum::make_map("one", x.one, "two", x.two);
    }
 
    [[nodiscard]] foo_type decode(datum const& x) const {
        return foo_type{ static_cast<int>(x["one"]), static_cast<int>(x["two"]) };
    };
};
 
hi::observer<foo_type> foo;
preferences.add("foo", foo);
 
hi_log_info("old: {}", foo->one);
foo->one += 1;
hi_log_info("new: {}", foo->one);