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A lightweight entity component system written in Kotlin.

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package com.github.quillraven.fleks.collection

import kotlin.math.max

/**
 * Creates a new [Bag] of the given [capacity] and type. Default capacity is 64.
 */
inline fun  bag(capacity: Int = 64): Bag {
    return Bag(arrayOfNulls(capacity))
}

/**
 * A bag implementation in Kotlin containing only the necessary functions for Fleks.
 */
class Bag(
    @PublishedApi
    internal var values: Array
) {
    var size: Int = 0
        private set

    val capacity: Int
        get() = values.size

    fun add(value: T) {
        if (size == values.size) {
            values = values.copyOf(max(1, size * 2))
        }
        values[size++] = value
    }

    operator fun set(index: Int, value: T) {
        if (index >= values.size) {
            values = values.copyOf(max(size * 2, index + 1))
        }
        size = max(size, index + 1)
        values[index] = value
    }

    operator fun get(index: Int): T {
        if (index < 0 || index >= size) throw IndexOutOfBoundsException("$index is not valid for bag of size $size")
        return values[index] ?: throw NoSuchElementException("Bag has no value at index $index")
    }

    /**
     * Returns the element at position [index] or null if there is no element or if [index] is out of bounds
     */
    fun getOrNull(index: Int): T? = values.getOrNull(index)

    fun hasNoValueAtIndex(index: Int): Boolean {
        return index >= size || index < 0 || values[index] == null
    }

    fun hasValueAtIndex(index: Int): Boolean {
        return index in 0.. Unit) {
        for (i in 0 until size) {
            values[i]?.let(action)
        }
    }
}