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Showing content from https://learn.microsoft.com/en-us/uwp/cpp-ref-for-winrt/map-view-base below:

winrt::map_view_base struct template (C++/WinRT) - Windows UWP applications

A base class from which you can derive to implement your own custom view, or span, of a contiguous sequence of elements in an associative collection. For more info, and code examples, see Collections with C++/WinRT.

Syntax

template <typename D, typename K, typename V, typename Version = winrt::impl::no_collection_version>
struct map_view_base : iterable_base<D, winrt::Windows::Foundation::Collections::IKeyValuePair<K, V>, Version>

Template parameters

typename D Your derived type name.

typename K The type of the keys in the collection that the map_view_base views, or spans.

typename V The type of the values in the collection that the map_view_base views, or spans.

typename Version A type that provides versioning policy and services to the collection.

Requirements

Minimum supported SDK: Windows SDK version 10.0.17763.0 (Windows 10, version 1809)

Namespace: winrt

Header: %WindowsSdkDir%Include<WindowsTargetPlatformVersion>\cppwinrt\winrt\base.h (included by default)

Member functions Iterators

A map_view_base is a range, and that range is defined by internal free functions (each of which retrieves an iterator) that are compatible with standard language features. Because of this, you can enumerate the elements viewed by a map_view_base object with a range-based for statement.

You can also retrieve an IIterator from the map_view_base::First function, and use that to iterate through the elements viewed by a map_view_base object.

...
#include <iostream>
using namespace winrt;
using namespace Windows::Foundation::Collections;
...
struct MyMapView :
    implements<MyMapView, IMapView<winrt::hstring, int>, IIterable<IKeyValuePair<winrt::hstring, int>>>,
    winrt::map_view_base<MyMapView, winrt::hstring, int>
{
    auto& get_container() const noexcept
    {
        return m_values;
    }

private:
    std::map<winrt::hstring, int> m_values{
        { L"AliceBlue", 0xfff0f8ff }, { L"AntiqueWhite", 0xfffaebd7 }
    };
};
...
IMapView<winrt::hstring, int> view{ winrt::make<MyMapView>() };

for (auto const& el : view)
{
    std::wcout << el.Key().c_str() << L", " << std::hex << el.Value() << std::endl;
}

IIterator<IKeyValuePair<winrt::hstring, int>> it{ view.First() };
while (it.HasCurrent())
{
    std::wcout << it.Current().Key().c_str() << L", " << std::hex << it.Current().Value() << std::endl;
    it.MoveNext();
}

map_view_base::First function

Retrieves an IIterator representing the first element viewed by the map_view_base object.

Syntax

auto First();

Return value

An IIterator representing the first element viewed by the map_view_base object.

map_view_base::HasKey function

Determines whether the specified key belongs to an element viewed by the map_view_base object.

Syntax

bool HasKey(K const& key) const noexcept;

Parameters

key The key to look for.

Return value

true if an element containing the key is found, otherwise false.

map_view_base::Lookup function

Looks up the element identified by the specified key, and retrieves the corresponding value.

Syntax

V Lookup(K const& key) const;

Parameters

key The key to look up.

Return value

The value corresponding to the key being looked up if found, otherwise a winrt::hresult_out_of_bounds exception is thrown.

map_view_base::Size function

Retrieves the number of elements viewed by the map_view_base object.

Syntax

uint32_t Size() const noexcept;

Return value

A value representing the number of elements viewed by the map_view_base object.

map_view_base::Split function

Splits the map view into two views.

Syntax

void Split(Windows::Foundation::Collections::IMapView<K, V>& first, Windows::Foundation::Collections::IMapView<K, V>& second) const noexcept;

Parameters

first One half of the original map.

second The second half of the original map.