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Evaluator Variables
The evaluator supports the following variable types:
| Type | Description | Minimum | Maximum |
|---|---|---|---|
| bool | boolean (true or false) | n/a | n/a |
| int | signed 32-bit integer | -2147483648 | 2147483647 |
| uint | unsigned 32-bit integer | 0 | 4294967295 |
| int64 | signed 64-bit integer | -9223372036854775808 | 9223372036854775807 |
| uint64 | unsigned 64-bit integer | 0 | 18446744073709551615 |
| double | double-precision floating point | 1.7E-308 | 1.7E+308 |
| date | date/time | 1601-01-01 00:00:00 | 9999-12-31 23:59:59 |
| str | string | n/a | n/a |
| path | path | n/a | n/a |
| map | value container | n/a | n/a |
When you initialise a variable, some types are inferred automatically:
| Example | Initialises as |
|---|---|
| x = true; | bool |
| x = false; | bool |
| x = 15; | uint |
| x = -15; | int |
| x = 5000000000; | uint64 |
| x = -5000000000; | int64 |
| x = 1185.15; | double |
| x = "string"; | str |
| x = [a = 1; b = 2;]; | map |
There are two ways you can explicity initialise a variable as a certain type. This is required for date and path variables which are always initialised from strings.
- You can use the As operator, for example d = "2023-08-20" as date;
- You can use the : operator, for example d: date = "2023-08-20";
For example, to initialise a variable as a path as opposed to a plain string:
p = "C:\Windows" as path; p = p + "System32"; Output(p); --> "C:\Windows\System32"
Note in the above example that the final string contains a backslash between "Windows" and "System32" - that's because it was initialised as a path variable, and adding strings to path variables adds path separators automatically.
See the documentation for the As operator for more details on explicit initialisation. The : operator uses the same type keywords as the As operator does.
The evaluator will implicitly convert variable types if needed. For example, if you call a function that's documented as taking an int but you pass it a uint, and int64 or even a str, the value will be converted automatically (assuming such a conversion is possible, of course).
You can use the TypeOf function to determine a variable's type.
Variable names
Ordinary variables must begin with a letter; after that, they can contain any number of letters, numbers or symbols like _ and $.
The evaluator also lets you access external variables that begin with a $ sign. For example, a function that uses @set name Jon and then invokes evaluator code would be able to access that variable using the name $name. External variables scoped to tabs and Listers can be accessed, for example $glob:name would let you get or set a globally scoped variable from within the evaluator.
Normally, attempting to use the value of a variable that doesn't exist causes an error, however for compatibility reasons, variables that begin with a $ allow this - if they haven't been previously defined they'll simply return an empty string.
You can also access environment variables from evaluation code as you can in normal functions. For example,
Output(%PROGRAMFILES%); --> C:\Program Files
You can set environment variables from evaluation code too but note that this only affects the environment inside Opus itself - globally the rest of the system won't see the changed value.
Numeric constants
You can express numeric constants in a number of ways:
- Plain decimal numbers such as 15 or -15.
- Hexadecimal numbers such as 0xe.
- Size values such as 5kb, 21gb, 1.75tb (note: only supports binary units.)
- Date units using suffixes h (hour), m (minute), s (second), d (day), M (month) and y (year) when adding to or subtracting from dates.
- Fractional numbers such as 1185.15.
- true and false are also available as boolean constants.
- pi is predefined as the value of π.
Value containers
A value container is a variable that can contain other variables - similar to a struct in C++ or a map in JavaScript.
Value containers are defined using the [ ] operator. The square brackets act like a scope - within the brackets, variables you assign will become members of the container. For example,
// defines an empty container x = [ ]; // defines a container with three members x = [ a = 5; b = 10; c = "hello!"; ];
After a value container is created and / or initialised, you can access its member variables (or add new ones) using the . operator.
Output(x.c); --> hello! x.c = Left(x.c, 5) + " world!"; Output(x.c); --> hello world!