Using Array-Like Structs As Arrays In Lucee CFML 5.3.7.47
The other day, when I was working on unifying type casting errors in Lucee CFML, I spent some time digging around in the Lucee source code on GitHub looking for examples of casting error messages. As I was doing this, I came across a Java class called StructAsArray. This wrapper class appears to allow array-like Structs to be treated as Arrays in some scenarios. I don't recall ever seeing this discussed; so, I wanted to perform a quick experiment in Lucee CFML 5.3.7.47.
Based on the code that I am seeing in the Java class, it looks like this "Arrayish" wrapper depends on the keys in the Struct being composed entirely of integer values. This makes sense since - depending on how hard you squint - an Array can be thought of as a Struct that associates numeric indices with values (and has a predictable iteration sequence).
That said, let's try to create a Struct with numeric keys and see what happens:
| <cfscript> | |
| arrayish = { | |
| 1: "First Value", | |
| 2: "Second Value", | |
| 3: "Third Value" | |
| // NOTE: Array-like structures with a "sparse" distribution of keys don't really | |
| // work the way they would with a true array. It seems they should be avoided. | |
| // -- | |
| // 10: "Sparse Value" | |
| }; | |
| // NOTE: Member-methods don't work consistently (since this is actually a Struct). As | |
| // such, BIFs (built-in functions) are safest for array-like structures. | |
| echo( "Length: #arrayLen( arrayish )# <br />" ); | |
| echo( "First: #arrayFirst( arrayish )# <br />" ); | |
| echo( "Last: #arrayLast( arrayish )# <br />" ); | |
| echo( "<br />" ); | |
| // Try looping using array-iteration. | |
| loop | |
| index = "i" | |
| value = "value" | |
| array = arrayish | |
| { | |
| echo( "#i# : #value# <br />" ); | |
| } | |
| arrayDeleteAt( arrayish, 1 ); | |
| arrayPrepend( arrayish, "Prepended value" ); | |
| arrayAppend( arrayish, "Appeneded value" ); | |
| echo( "<br />" ); | |
| dump( arrayish ); | |
| </cfscript> |
As you can see, our Struct variable, arrayish, is just a normal Struct that happens to have keys that look like array indices. Of course, the object is still a Struct, which means that the member methods are all "struct" member methods. As such, we have to use the Built-In Functions (BIFs) for Arrays in to get this wrapper behavior for Structs to work.
That said, when we run the above code, we get the following output:
As you can see, since our Struct looks like an Array, we can treat it like an array in a subset of Array use-cases.
To be honest, I don't have an immediate use-case for this. It was just a curiosity. I assume this is something that Lucee CFML is using internally? Does anyone have a good example of where something like this might be helpful?
Want to use code from this post? Check out the license.
Reader Comments
@All,
I wonder now if it would make sense for ColdFusion to just have an
arrayFrom()built-in function:www.bennadel.com/blog/4258-for-consideration-an-arrayfrom-function-in-coldfusion.htm
... something that could take array-like and other iterable values and turn them into native ColdFusion arrays.