CFML higher-order functions compared to tag-based code: some, every and each functions

G'day:

I'm gonna try to round out this short series today: there's not much to say about the some, every and each methods in the context of comparing their functionality to old-school tag-based code. As a reminder, I've already covered map, reduce, filter and sort operations.

some

some iterates over the collection, calling a callback on each element, and will exit as soon as the callback returns true for an element. An example might be checking if at least some class members passed (or failed) their test:

examResults = [
    {person="Alex", mark=75},
    {person="Billie", mark=52},
    {person="Charlie", mark=41},
    {person="Daryl", mark=29},
    {person="Evan", mark=53}
]

somePassed = examResults.some((result) => result.mark >= 50)

writeOutput("Some of the class passed the test? #somePassed#<br><hr>")


someFailed = examResults.some((result) => {
    writeOutput("Called for #result.person#, #result.mark#<br>")
    return result.mark < 50
})

In the second example there I show a difference between this iteration function and the others we've encountered so far. All the others always iterate through the entire collection, however some and every do not. They exit as soon as they can answer the question. So as soon as some gets a true it exits; as soon as every gets a false it exits. The output of this is:

Some of the class passed the test? true

---

Called for Alex, 75
Called for Billie, 52
Called for Charlie, 41

In this case it only got as far as the first false result from the callback (because, sadly, Charlie did not make the cut)

The tag-based version of this would be:

<cfset somePassed = false>
<cfloop array="#examResults#" item="result">
    <cfif result.mark GTE 50>
        <cfset somePassed = true>
        <cfbreak>
    </cfif>
</cfloop>
<cfoutput>Some of the class passed the test? #somePassed#<br><hr></cfoutput>

<cfset someFailed = false>
<cfloop array="#examResults#" item="result">
    <cfoutput>Called for #result.person#, #result.mark#<br></cfoutput>
    <cfif result.mark LT 50>
        <cfset someFailed = true>
        <cfbreak>
    </cfif>
</cfloop>

Again with the boilerplate code (ref from previous articles).

BTW, don't get carried away with these higher-order functions if there's another built-in function to do the job. Recently I checked if something was in an array by doing this:

colours = ["Whero","Karaka","Kowhai","Kakariki","Kikorangi","Poropango","Papura"]

containsGreen = colours.some((colour) => colour == "Kakariki")
writeOutput("It contains green: #containsGreen#<br>")

My boss gently pointed out I could just do this:

containsGreen = !!colours.find("Kakariki")

Use the simpler option where possible ;-)

every

every is the opposite of some: it exits as soon as the callback returns false. Our example here would be to check if everyone passed the exam:

everyonePassed = examResults.every((result) => {
    writeOutput("Called for #result.person#, #result.mark#<br>")
    return result.mark >= 50
})
writeOutput("Everyone passed the test? #everyonePassed#<br><hr>")

Called for Alex, 75
Called for Billie, 52
Called for Charlie, 41
Everyone passed the test? false

---

The tag-based equivalent is the usual "mostly boilerplate" thing:

<cfset everyonePassed = true>
<cfloop array="#examResults#" item="result">
    <cfoutput>Called for #result.person#, #result.mark#<br></cfoutput>
    <cfset personPassed =  result.mark GTE 50>
    <cfif NOT personPassed>
        <cfset everyonePassed = false>
        <cfbreak>
    </cfif>
</cfloop>
<cfoutput>Everyone passed the test? #everyonePassed#<br><hr></cfoutput>

each

Sometimes it's not a data transformation that one needs when iterating over a collection. If none of the other options do the trick, there's the generic each method:

examResults.each((result) => {
    writeOutput("Name: #result.person#, mark: #result.mark#<br>")
})

As a general rule never start solving an iteration task with each. Consider if one of the other more situation-specific methods are a better fit. It's seldom that each is the right answer.

And the tag equivalent is pretty much the same, because - really - all the tag version does is "each"; it's down to the inner code block to distinguish between the various iteration possibilities:

<cfloop array="#examResults#" item="result">
    <cfoutput>Name: #result.person#, mark: #result.mark#<br></cfoutput>
</cfloop>

OK that's it. Tag-based CFML versions of the more situation-descriptive and less boilerplate iteration higher-order functions. If you need anything else about them explained, let me know.

Righto.

--
Adam