Mod:Creation Kit/Operator Reference

The following are valid operators in the Papyrus language:

[], =  +  - *  /  %  .  "" ! == != >  <  >= <= || && += -= *= /= %= as is

Parenthesis
Parenthesis, when surrounding an expression, will cause that expression to be evaluated before any operators outside of the parenthesis. When following a function name, they denote the parameter list for the function.

Examples: i = (1 + 2) * 3 MyFunction(10)
 * i will get the value of 9
 * call the function MyFunction with a parameter of 10

Square Brackets
[] Square brackets are used for arrays. Either for accessing a specific array element, denoting the size of an array for a new one, or for denoting that a type is an array type.

Examples: i = myArray[0] int[] myArray = new int[10]
 * i whatever is in element 0 of the array
 * define an array of size 10

Comma
, The comma operator separates parameters in a function definition, or a function call.

Examples: MyFunction(10, 20)
 * call the function MyFunction with a parameter of 10 and 20

Math Operators
+ - * / % Math operators perform some sort of operation on the two expressions it sits between. Papyrus supports assignment, addition, subtraction, multiplication, division, and integer modulus. The minus sign is also used for negation (also known as unary minus). The addition operator can also be used to concatenate ('paste together') strings.

Examples: i = 1 + 2 * 3 i = 9 % 4 i = "Hello " + "World"
 * i will get the value of 7
 * i will get the value of 1
 * i will get the string "Hello World"

Note
In the past, there was concern about the correctness of the modulo operator when applied to negative integers such as -2,147,483,647 (0x80000001). Those concerns were unfounded.

The modulo operator produces correct results in all cases, but it must be understood that the result will have the sign of the dividend in Papyrus (as in Java and many other languages), therefore  and.

A specific case of concern was the calculation necessary to isolate the low-order 3 bytes (6 nibbles, or 24 bits) of an integer, which requires a modulo operation with a divisor of 2^24 (AKA 0x01000000 or 16,777,216). When that modulo operation is applied to dividends in the range -2,147,483,647 (0x80000001) to -1 (0xFFFFFFFF), inclusive, the results correctly range from -16,777,215 (0xFF000001) to -1 (0xFFFFFFFF). However, the goal of isolating the low-order 3 bytes of the integer (performing an operation equivalent to a bit-wise AND with 0x00FFFFFF) is not met in those cases. In order to meet that goal, negative values must be handled specially. For example:

int Function getLow3Bytes(int i) {Set the high 8 bits of i to zero, and return the low 24 bits intact. Equivalent to "i & 0x00FFFFFF" in C, Java, etc.} if i < 0 ; Force i to be a positive number, by changing its high bit (bit 32) from 1 to 0. i += 0x80000000 endIf return i % 0x01000000 EndFunction

Such emulation of bit-wise operations using mathematical operations is a little more complicated when the high bit must be preserved:

int Function getHighByteAsLowByte(int i) {Return the high byte of i as a value between 0 and 255 (0x00-0xFF), inclusive. Equivalent to "i >> 24 & 0xFF" in C, Java, etc.} if i < 0 ; Force i to be a positive number, by changing its high bit (bit 32) from 1 to 0. ; Then divide by 0x01000000 (16,777,216), which is now equivalent to a right shift of 24 bits. ; Finally, restore the value of the high bit we cleared, now that it is bit 8 and cannot affect the sign. return (i + 0x80000000) / 0x01000000 + 0x80 endIf return i / 0x01000000 EndFunction

Dot
. The dot operator goes after a variable name to let you call functions on it, or to access properties or struct members.

Examples: myVariable.MyFunction myVariable.MyProperty = 10
 * Call the function on the variable
 * Set the property to 10

Double Quotes
"" Double quotes surround a string literal.

Examples: hello = "Hello World!"
 * A basic hello world string

Logical Operators
! || && Logical operators evaluate to true or false values, based on their expressions.
 * The NOT operator (!) will be true if its single expression (to the left of the operator) is false, and false if it is true.
 * The OR operator (||) will be true if one of the expressions to its left and right are true, and will short-circuit if the left expression is true (it will not evaluate the right expression at all).
 * The AND operator (&&) will be true if both of the expressions to its left and right are true, and will short-circuit if the left expression is false (it will not evaluate the right expression at all).

Examples: i = a && b i = !a
 * i gets true if both a and b are true
 * i gets true if a is false

Comparison Operators
== != < > <= >= The comparison operators compare both expressions to their left and right, and return a boolean value based on the operator used. If floating-point values are being compared, a tiny epsilon value is accounted for to conteract floating-point error. If string variables are being compared, the comparison is case-insensitive.
 * Equality (==) returns true if both expressions have equal values.
 * Inequality (!=) returns true if both expressions have inequal values.
 * Less-than (<) returns true if the right expression's value is smaller then the left expression's value.
 * Greater-than (>) returns true if the right expression's value is larger then the left expression's value.
 * Less-than or equal to (<=) returns true if the right expression's value is smaller than or equal to the left expression's value.
 * Greater-than or equal to (>=) returns true if the right expression's value is larger than or equal to the left expression's value.

Examples: i = a > b i = a == b
 * i will get true if a is greater then b
 * i will get true if a is equal to b

Assignment Operators
= += -= *= /= %= Assignment operators assign the value from the right expression to the variable (or property) from the left expression. If the equal sign starts with one of the math operators, then the right expression's value will be added to the current value of the left expression, and then assigned to the left expression. Note that if the left expression is a property, then both the property's get and set functions will be called.

Examples: i = 10 i += 1
 * assign 10 to i
 * add 1 to the current value of i, and assign it to i

Cast
as The cast operator attempts to cast the value from the left expression to the type to the right of it, and returns the resulting value.

Examples: i = a as float
 * cast a to a float and assign it to i

Type Check
is The type check operator checks to see if the value from the left expression is the type specified to the right of it, and returns true or false. If the type is a base type, like int, bool, or float, the check is strict and will only return true if the type exactly matches (a float is not an int, for example). If the type is an object type, then the check is loose and will return true if the object would be successfully cast to the type (an ObjectReference is a Form).

Examples: if myObject is ObjectReference Debug.Trace("I got an object reference!") endIf
 * check to see if myObject is an ObjectReference

Operator Precedence
Operator precedence is listed in the following table, from highest to lowest: