HashMap Manual


maxon::HashMap is a generic class template for a map that maps keys to values with the help of hash values. It can use data types as a key that implement a "GetHashCode" and "IsEqual" function. maxon::HashMap is based on maxon::MapBase and maxon::Collection.


A new hash map object can simply be created using the class template:

// This example creates a hash map and inserts two elements.
// The hash map stores maxon::String values using maxon::Int keys.
atoms.Insert(1, "Hydrogen"_s) iferr_return;
atoms.Insert(2, "Helium"_s) iferr_return;

The data stored in a maxon::HashMap can be cleared with:


An entry in a maxon::HashMap is represented as a maxon::HashMap::Entry object. New entries can be inserted with:

// This example creates a hash map and inserts elements in various ways.
// insert data
atoms.Insert(1, "Hydrogen"_s) iferr_return;
// insert data
maxon::Bool created = false;
auto e = &atoms.InsertEntry(2, created) iferr_return;
if (created && e)
// insert data
maxon::String& str = atoms.InsertKey(3, created) iferr_return;
str = "Lithium"_s;
// insert data
return maxon::OK;
atoms.InsertLambda(4, lambda) iferr_return;
// insert data (multi-map)
if (e)

An entry stored in the maxon::HashMap can be found using the proper key:

// This example gets the values for a given keys in the hash map.
// find key "1"
auto e = atoms.Find(1);
if (e)
// find key "2"
const maxon::String* const str = atoms.FindValue(2);
if (str)

An entry of the maxon::HashMap can also be deleted:

// This example searches the entry for the given key and deletes it.
// find entry for key "1"
e = atoms.Find(1);
if (e)
atoms.Erase(e, true) iferr_return;

It is easily possible to iterate trough all stored key and values with:

See also Iterate.

// This example loops through all keys and value of the given hash map
// and the multi-map values of a given key.
// list all keys
for (const maxon::Int& key : atoms.GetKeys())
DiagnosticOutput("Key: @", key);
// list all values
for (const maxon::String& value : atoms.GetValues())
DiagnosticOutput("Values: @", value);
// list multi-map values of given key
for (const auto& it : atoms.FindAll(1))
const auto value = it.GetValue();
DiagnosticOutput("Value: @", value);

A maxon::HashMap stores a certain number of elements and has a certain capacity to store further elements:

// This example reads data from the given hash map.
const maxon::Int count = atoms.GetCount();
const maxon::Int nonEmptyCount = atoms.GetNonEmptyBucketCount();
const maxon::Int tableSize = atoms.GetTableSize();


It is easily to iterate over all entries in the maxon::HashMap:

// This example loops through all entries of the given hash map.
// loop through all key/value pairs
for (const auto& e : atoms)
const maxon::Int& key = e.GetKey();
const maxon::String& value = e.GetValue();
DiagnosticOutput("Key: @, Value: @", key, value);
auto e = atoms.Find(1);
if (e)
auto it = atoms.GetIterator(e);
// next element
const maxon::Int& key = it.GetKey();
const maxon::String& value = it.GetValue();
DiagnosticOutput("Key: @, Value: @", key, value);


A maxon::HashMap can easily be copied:

Further utility functions are:

Further Reading