unity-indexing's Introduction

Collections Indexing

Indexed foreach loops with minimal overhead.

Problem

Suppose you want a foreach loop but you also need the index of each element. You could keep track of the index yourself, but that's error prone especially when using continue.

int index = 0;
foreach (var item in collection)
{
    Process(item, index);
    index++;
}

The suggested solution on StackOverflow uses Select with index and anonymous types to achieve the desired result, but that causes memory allocation for every element.

foreach (var entry in collection.Select((item, index) => new { item, index }))
{
    Process(entry.item, entry.index);
}

This package provides an allocation-free alternative.

Usage

foreach (var (item, index) in items.Indexed())
{
    Process(item, index);
}

Performance

Iterating over 100,000 integers.

Collection	Method	GC Alloc B	Time ms
List	`for`	0	0.79
List	`foreach` (optimized)	0	1.42
List	`foreach`	40	1.42
List	Indexed	40	3.44
List	Wrap coroutine	104	3.47
List	Select ValueTuple	120	4.81
List	Select KeyValuePair	120	5.55
List	Select anonymous	2.3 M	16.06
List	Select Tuple	2.3 M	17.07

Collection	Method	GC Alloc B	Time ms
Array	`for`	0	0.23
Array	`foreach` (optimized)	0	0.27
Array	`foreach`	32	2.21
Array	Indexed	32	3.99
Array	Wrap coroutine	96	4.42
Array	Select ValueTuple	112	5.87
Array	Select KeyValuePair	112	6.43
Array	Select anonymous	2.3 M	16.85
Array	Select Tuple	2.3 M	18.14

Collection	Method	GC Alloc B	Time ms
Enumerable.Range	`foreach`	36	1.34
Enumerable.Range	Indexed	36	3.36
Enumerable.Range	Wrap coroutine	100	3.44
Enumerable.Range	Select ValueTuple	116	4.77
Enumerable.Range	Select KeyValuePair	116	5.57
Enumerable.Range	Select anonymous	2.3 M	15.99
Enumerable.Range	Select Tuple	2.3 M	17.04