The Case for Comma-Leading Lists

Introduction

Comma-leading lists are an objectively better presentation style.

They make logical sense; the next value on the list is dependant on the comma, and so, they should be kept together.

The style may look alien at first, but give it a test drive and you'll be surprised at how quickly it starts to look normal.

For now, let's have a look at the benefits.

Justification

1. No Merge Conflicts

When adding a new value to a list with trailing commas, you're making 2 additions and 1 deletion.

This will give you a merge conflict just because someone else adds a value on a different branch.

By using the comma-leading style, you make 1 addition and 0 deletions.

These commits play ball with each other, without needing any conflict resolution.

"Ah, but I've used a dangling comma," you say? Allow me to continue.

2. Dangling Commas Bad

It's true that using a trailing comma after the final value will prevent conflicts, but it's dumb for two reasons.

1. Language Inconsistency

SQL doesn't support them.

The JSON standard and Pre-ES5 JavaScript don't support them.

It's better to stick to a style that works across more languages, especially for a multi-lingual codebase.

2. Redundant Logic

There's not a second element. It's unnecessary context, so why justify it?

And, if an interpreter ever decides to stick a None in there, good luck.

3. Better Presentation

Separating Context

With the comma-leading style, the logic stays on the left, and the data stays on the right.

This makes it quicker and easier to scan when looking through code.

It will also allow you to quickly identify logic errors, such as missing commas.

Saving Whitespace

When you indent after the opening bracket, you're adding extra columns of whitespace on the left-hand side.

Placing the commas on the left keeps the code neat and narrow. Neat!

Summary

Comma-leading lists are easier for source control, more compatible across languages, and much faster to read since they keep data separate from the list's logic.

Do the world a favour and switch to a better standard of data structure.

animals = [ "ant"          , "bat"          , "cat"          , "dog"          ]

What's not to love?

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