Maps in UnrealScript

Maps are Unrealscript’s built-in associative data type, sometimes called hashes or dicts in other languages.

To create an empty map, use the default keyword:

class MyMapExample extends Object;

function CreateEmptyMap()
{
    local map<string, int> MyMap;
    MyMap.default;
}

Set key/value pairs using typical MyMap[key] = val syntax.

function SetValues()
{
    local map<string, int> MyMap;
    MyMap("k1") = 7;
    MyMap("k2") = 13;
    `log("MyMap: " @ MyMap);
}

Printing a map will show all of its key/value pairs.

function PrintMap()
{
    local map<string, int> MyMap;
    MyMap("k1") = 7;
    MyMap("k2") = 13;
    `log("MyMap: " @ MyMap);
}

defaultproperties
{
    MyMap=(("k1", 7), ("k2", 13))
}

Get a value for a key with MyMap[key].

function GetValue()
{
    local map<string, int> MyMap;
    local int v1;
    MyMap("k1") = 7;
    v1 = MyMap("k1");
    `log("v1: " @ v1);
}

If the key doesn’t exist, the zero value of the value type is returned.

function GetValueForNonExistingKey()
{
    local map<string, int> MyMap;
    local int v3;
    MyMap("k1") = 7;
    v3 = MyMap("k3");
    `log("v3: " @ v3); // Output will be 0
}

The builtin Len returns the number of key/value pairs when called on a map.

function LenOfMap()
{
    local map<string, int> MyMap;
    MyMap("k1") = 7;
    MyMap("k2") = 13;
    `log("len: " @ MyMap.Length());
}

The builtin Remove removes key/value pairs from a map.

function RemoveKey()
{
    local map<string, int> MyMap;
    MyMap("k1") = 7;
    MyMap("k2") = 13;
    MyMap.Remove("k2");
    `log("MyMap: " @ MyMap);
}

To remove all key/value pairs from a map, use the Clear method.

function ClearAllKeys()
{
    local map<string, int> MyMap;
    MyMap("k1") = 7;
    MyMap("k2") = 13;
    MyMap.clear();
    `log("MyMap: " @ MyMap);
}

The optional second return value when getting a value from a map indicates if the key was present in the map.

function CheckKeyPresence()
{
    local map<string, int> MyMap;
    local bool prs;
    local int _;
    
    MyMap("k1") = 10;

    (_, prs) = MyMap.Find("k2");
    `log("prs: " @ prs); // Output will be false
}

You can also declare and initialize a new map in the same line with this syntax.

function InitializeMap()
{
    local map<string, int> MyMap;
    MyMap = (("foo", 1), ("bar", 2));
    `log("MyMap: " @ MyMap);
}

The maps package contains a number of useful utility functions for maps.

function MapEqualityCheck()
{
    local map<string, int> Map1, Map2;

    Map1 = (("foo", 1), ("bar", 2));
    Map2 = (("foo", 1), ("bar", 2));

    if (MapsEqual(Map1, Map2))
    {
        `log("Map1 == Map2");
    }
}

function bool MapsEqual(map<string, int> Map1, map<string, int> Map2)
{
    local string key;
    foreach Map1.Keys(key)
    {
        if (Map1[key] != Map2[key])
            return false;
    }
    return true;
}

Now you have learned about maps in Unrealscript, their basic operations, and some utility functions. Next, you can explore more about the language.

Slices in UnrealScript

Functions in UnrealScript

Learn X By Example

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Maps in UnrealScript