diasurgical/devilutionX

Make custom iterators for activ entity lists

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#2586 opened on Aug 12, 2021

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good first issuehelp wanted

Description

There are a lot of loops that we are not able to convert to ranges as they only loop over the active entities rather then all entities.

	for (int i = 0; i < ActiveMissileCount; i++) {
		int mx = ActiveMissiles[i];
		if (Missiles[mx]._mitype == MIS_TOWN && missile._misource == id)
			Missiles[mx]._mirange = 0;
	}

This also means that we will still be indexing in to the global array at least once.

To solve this we can create custom iterators:

	for (auto missile : ActiveMissileIterator) {
		if (missile._mitype == MIS_TOWN && missile._misource == id)
			missile._mirange = 0;
	}

https://internalpointers.com/post/writing-custom-iterators-modern-cpp

Some times it may also be useful with iterators that can take a custom range:

	int start = gbIsMultiplayer ? 3 : 2;
	int end = gbIsHellfire ? 10 : 8;
	for (auto healitem : ItemIterator(&Healitems[start], &Healitems[end])) {
		healitem._iCreateInfo = lvl | CF_HEALER;
		healitem._iIdentified = true;
		healitem._iStatFlag = StoreStatOk(&healitem[i]);
	}

This issue builds on the changes done in https://github.com/diasurgical/devilutionX/issues/2435 but does not strictly require it.

Contributor guide

Tech stack
cpp
Domain
backend
Issue type
refactor
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-3 hours
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
C++ knowledgeiterator basics
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
40
Research direction
The issue proposes creating custom iterators for active entity lists (e.g., ActiveMissiles) to replace index based loops. Refer to the linked issue #2435 for context on related changes. The article at https://internalpointers.com/post/writing custom iterators modern cpp provides a guide. Implementation should follow the examples in the issue description, possibly extending to other entity types like items. No current assignee or PR exists, so the work is available.