Structs are one of the core data structures in Adobe ColdFusion, but if you’re coming from another language the term might sound a little strange at first. Say “struct” to a JavaScript, Python, or Java developer and you may get a confused look, even though they use very similar things every day. In this post we’ll unpack what a struct is in ColdFusion, why it’s so useful, and where you need to be a little careful when using it.

At its simplest, a struct is just a collection of key–value pairs. If you think of an array as a row of numbered buckets (index 1, 2, 3, …), a struct is a set of buckets that each have a name instead of a number. Instead of saying “give me bucket 1”, you say “give me the bucket named name or email.” Keys are strings (alphanumeric) and they point to whatever values you want to store: strings, numbers, arrays, even other structs.

If you’ve used dictionaries in Python, objects in JavaScript, hashes in Ruby, or maps in Java, you already understand the idea. Almost every language has some version of “named buckets” because it’s incredibly convenient. Structs let you group related data under meaningful labels, which makes your code easier to read and your intent much clearer than if you were juggling a bunch of “slot 1 / slot 2 / slot 3” style values.

There is an important twist, though: by default, ColdFusion structs are unordered. That means if you insert keys in the order name, address, phone, email and then later loop over that struct, ColdFusion makes no promise that you’ll get them back in that same sequence. Under the hood, unordered structs are optimized for performance, not for preserving insertion order. In many cases this is perfectly fine, especially when you already know the keys (name, email, etc.) and you’re just grabbing them directly.

Sometimes, however, order really does matter. Imagine you’re building a grid or table where each key becomes a column: you probably want Name, Email, Phone, City in a consistent order instead of a random shuffle every time the page loads. For those cases, ColdFusion lets you create an ordered struct. You take a small performance hit, but on modern hardware it’s usually negligible, and in return you get stable, predictable ordering for things like reports, grids, or any user-facing display where column order affects usability.

Another default behavior to know about is case sensitivity. Out of the box, struct keys in ColdFusion are case-insensitive. That means user.name, user.Name, and user.NAME all refer to the same key. Often this is a good thing, because you’re not outputting the key names directly and you don’t really care about their exact casing. But sometimes, especially when you’re using keys as labels (e.g., turning them into column headings), the difference between FirstName and firstname actually matters. In those cases, ColdFusion lets you create case-sensitive structs, and even structs that are both ordered and case-sensitive, so you can control both aspects when your design calls for it.

At a glance, a struct literal can look a lot like JSON, and it’s tempting to treat them as interchangeable. They’re closely related but not identical. Through serialization and deserialization you can move data between structs and JSON very easily, but there are subtle differences in how things like case, ordering, and certain data types are handled. If you bounce data back and forth between JSON and structs “just because it works,” you can sometimes get surprising changes in keys or values. The takeaway: use the serialization functions deliberately, and don’t assume that “valid JSON” and “ideal ColdFusion struct” are always the same shape.

So when should you reach for a struct? A classic example is an address book entry. Each contact might have name, address, phone, email, and so on. That one “row” of data is a perfect fit for a single struct. If you have many contacts, you’ll often model that as an array of structs: each element in the array is one contact struct with the same set of keys. This pattern — grouping logical fields into a struct, and then storing lots of those structs in an array — is one of the most powerful combinations in ColdFusion.

Structs also shine whenever you have consistent key names that make more sense than numeric positions. For example, user input from a form: firstName, lastName, email, newsletterOptIn. You could cram those into an array at positions 1, 2, 3, 4, but then you’re stuck remembering what “slot 3” means months later. With a struct, you can think in terms of meaning instead of position, which makes your code more self-documenting and less error-prone.

That said, structs aren’t always the right tool. They’re powerful — sometimes a bit like using a sledgehammer when all you needed was a ball-peen. The distinction between ordered and unordered, case-sensitive and non-case-sensitive, and how the data will eventually be used all require a bit of planning. In some scenarios a simple array, a ColdFusion query object, or a custom CFC might better match your data model. Structs tend to work best as part of a hybrid approach: arrays of structs, structs of structs, or structs alongside queries, each doing what they’re best at.

Finally, remember that structs are real objects in memory, not just syntax sugar. Clearing a struct doesn’t make the object magically vanish; an empty struct is still a struct, and if you create and clear millions of them in a long-running application (think chat sessions, API calls, or heavy background processing), you can create unnecessary memory pressure. ColdFusion gives you a rich set of built-in struct functions to inspect, count, and manage your structs efficiently — use those tools thoughtfully and you’ll avoid subtle bugs and leaks.

In the next section (and in the accompanying video), we’ll get into concrete CFScript examples that show how to create structs, nest them, iterate over them, and combine them with arrays and JSON in real-world ColdFusion applications. For now, if you understand that structs are named buckets of related data — with important behaviors around ordering, case, JSON, and memory — you’ve got the mental model you need to start using them effectively.

For a detailed look at how to use Structs effectively, please take a look at my Foundations webinar on our YouTube channel here: https://www.youtube.com/watch?v=LpokGqYOT9whttps://www.youtube.com/watch?v=LpokGqYOT9w

You can find the code and “Struct factory” code at my GitHub here: 
https://github.com/AdobeColdFusion/webinars/tree/main/structshttps://github.com/AdobeColdFusion/webinars/tree/main/structs