fields.md

layout	default
title	Adding fields
parent	Usage
nav_order	3
description	Extending classes and adding fields

Fields

Say you want to add a property to an existing class. One way you could do this is by storing the property in a global variable like so:

int totalJumps = 0;

class $modify(PlayerObject) {
    void pushButton(PlayerButton button) {
        Interface::mod()->log() << "the player has jumped " << totalJumps << " times !" << geode::endl;
        totalJumps++;
        $PlayerObject::pushButton(button);
    }
};

This works; however, it isn't ideal. The counter never resets back down to 0, and the same value is shared across all instances of PlayerObject.

One could solve this problem by using the setUserData function in CCNode or by utilizing more complicated systems, but both solutions are less than ideal.

Geode provides a better alternative: field_t. field_t helps add new instance variables to modified classes. Take a look at an example:

class $modify(PlayerObject) {
    field_t<int> m_totalJumps;

    void pushButton(PlayerButton button) {
        Interface::mod()->log() << "the player has jumped " << this->*m_totalJumps << " times !" << geode::endl;
        (this->*m_totalJumps)++;
        $PlayerObject::pushButton(button);
    }
};

This code works even if you have multiple PlayerObjects, and the counter is initialized as 0 for each one, providing an elegant yet simple solution to the problem.

However, field_t does come with some quirks when it comes to accessing the value of the field.

• field_t values can only be accessed using the access operator ->*. In other words, this->*m_field is required to read or write to the field.
• Due to the operator precedence of ->*, sometimes you will have to wrap the access operator in parenthesis. You can see an example of this in the previous code block ((this->*m_totalJumps)++).

If you need a default value, you can just set it just like you would for a normal field.

class $modify(PlayerObject) {
    field_t<int> m_totalJumps = 13; // Starts the amount of jumps at 13

    void pushButton(PlayerButton button) {
        Interface::mod()->log() << "the player has jumped " << this->*m_totalJumps << " times !" << geode::endl;
        (this->*m_totalJumps)++;
        $PlayerObject::pushButton(button);
    }
};