Sanford Whiteman

The only time you should use the + sign in Velocity instead of $math.add()

Blog Post created by Sanford Whiteman on Oct 14, 2019

For arithmetic in Velocity, the only safe approach is the so-called “tools-ish” one: use MathTool methods like $math.add, $math.sub, and  $math.mul.

 

The rule

Aside from the one exception later in this post, you should not use the Java-like math operators (+ and -).

 

The core reason is the plus sign + and minus sign - have different syntax rules in Velocity! You can easily create fatal errors – or worse, lines that are silently ignored – by forgetting that - must be surrounded by spaces.

 

That’s right, only one of these is correct Velocity syntax for subtraction:

 

#set( $a = 99 )
#set( $b = $a - 1 ) ## correct
#set( $b = $a -1 ) ## fatal ParserException!
#set( $b = $a- 1 ) ## fatal ParserException!
#set( $b = $a-1 ) ## non-fatal, but doesn’t subtract!!!

 

So I always teach people to use #set( $b = $math.sub($a,1) ). It’s longer, but you’ll never break your code by switching sub and add.

 

The exception

Despite the above, in the course of developing my Base64 encoding in Velocity code, I discovered a unique requirement that could only be met by purposely using the + operator instead of $math.add.

 

This is the only exception I’ve found, and it doesn’t override my recommendation above. But it is – to me and I hope to the couple of people like me out there – fascinating.

 

So.

 

In Base64 encoding, one of the steps requires Integers to be converted to binary Strings, 42 → “00101010”. (If this is complete gibberish to you, you can reread this post when you have a couple more years of development under your belt!)

 

To get those Integers, you need to convert signed Bytes (-128 through 127) to their equivalent all-positive Integers (0 through 255).

 

To convert signed Bytes, you need to use a bitwise AND. But the traditional AND operator, the & symbol in Java and most other languages, isn’t available in Velocity.

 

Since you can’t use notation like #set( $c = $a & $b ) in Velocity (that’s a fatal parser error) you need to find a method-based way – a “tools-ish” way, somewhat ironically – to do a bitwise AND: something like #set( $c = $a.and($b) ).

 

Miraculously, such a method does exist (after you do some hunting) so long as $a is a Java BigInteger.  

 

Hmm. So now you need to be able to construct a BigInteger from an Integer.

 
Getting a BigInteger

A BigInteger isn’t something you can explicitly create in Marketo’s Velocity (post-June 2019, that is), only implicitly. There’s one way to cheat it, and that is to set a variable to just outside of the range of a Long. If you know off the type of your head that the max positive Long is 9,223,372,036,854,775,807 (~9 quintillion) then you can add 1 to that:
    

#set( $aBigInteger = 9223372036854775808 )
${aBigInteger.class} ## will be class java.math.BigInteger

 

 

Skipping the magic

But let’s say you don’t know that magic number – you only know that Java’s

concrete integer Number types  are, in order of increasing width, Byte → Short → Integer → Long → BigInteger. (I think it’s reasonable for a developer to know that progression, but not reasonable to expect someone to remember that 9,223,372,036,854,775,807 is special.)

 

If you didn’t know the magic Long-BigInteger boundary, how would you make sure Velocity allocated a type big enough for a BigInteger? You’d want to say:

 

Gimme a Number that can hold Long.MAX_VALUE + 1.

 

Of course to do that, you‘d have to get a handle on a Long (in order to refer to the constant Long.MAX_VALUE). Since Velocity doesn’t give you a Long unless you’ve asked for something bigger than an Integer, you have to say:

 

First, gimme a Number with the value 0. I know that’s an Integer, since that’s the default type for whole numbers in Velocity.


Then, gimme another Number that can hold ThisMustBeAnInteger.MAX_VALUE + 1. That’s gonna be a Long.

 

Finally, gimme yet another Number that fits ThisMustBeALong.MAX_VALUE + 1. That third number must be a BigInteger.

 

And here is where + acts differently from $math.add.

 

MathUtils vs. MathTools

Hidden in the doc for Velocity’s MathUtils (part of Velocity’s internal API, not for public consumption) you’ll find this gem:

 

So now we know Velocity can do – in fact is explicitly documented to do – exactly what we need. If we add 1 to the max value of a Long, the result will be a BigInteger (and will also have the correct value, obviously).

 

Except this only applies to the literal + operator. MathTools’ $math.add also does addition, but doesn’t implement the “overflow correction” logic.

 

Let’s compare.

 

Using the + operator:

#set( $Integer = 0 )
Integer $Integer.class.getName() = $Integer
#set( $Long = $field.in($Integer).MAX_VALUE + 1 )
Long $Long.class.getName() = $Long
#set( $BigInteger = $field.in($Long).MAX_VALUE + 1 )
BigInteger $BigInteger.class.getName() = $BigInteger

 

The output will be:

Integer java.lang.Integer = 0
Long java.lang.Long = 2147483648
BigInteger java.math.BigInteger = 9223372036854775808


Exactly what we need. $BigInteger is a BigInteger we can use as a factory to make more BigIntegers ($BigInteger.valueOf) and then do fancy stuff like .and() and .or() and  .xor() which would otherwise be impossible in Velocity.

 

Let’s try using $math.add:

#set( $Integer = 0 )
Integer $Integer.class.getName() = $Integer
#set( $Long = $math.add($field.in($Integer).MAX_VALUE,1) )
Long $Long.class.getName() = $Long
#set( $BigInteger = $math.add($field.in($Long).MAX_VALUE,1) )
BigInteger $BigInteger.class.getName() = $BigInteger

 

 

The output will be:

Integer java.lang.Integer = 0
Long java.lang.Long = 2147483648
BigInteger java.lang.Long = 9223372036854775807

 

 

Whoa. We attempted to add 1 to the largest Long, but the attempt silently failed. $BigInteger (despite the name) remains a Long, and it never gets incremented: it’s still Long.MAX_VALUE or 9,223,372,036,854,775,807.

 

It’s notable, but doesn’t change the rule

The likelihood that you’d otherwise need to perform BigInteger-range arithmetic within Marketo is basically zero.

 

I mean, it would have to be something like… you’re using a webhook to take the squares of lead scores, and you have a score in the millions and must raise it to the power of 2 in a Velocity token. Let’s face it, relative to the chances you will at some point forget the spaces around -, that’s just not gonna happen.  The risk/reward overwhelmingly favors $math.add and $math.sub.

 

In this case we needed a BigInteger not because of its infinite range of values, but because we need to get at the cool methods it has – which Integers and Longs do not. (The underlying value is tiny, between -128 and 127 then converted to between 0 and 255.) So for this particular purpose, deliberately using + makes sense.

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