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Operators

The Alloy configuration syntax uses a common set of operators. All operations follow the standard PEMDAS order of mathematical operations.

Arithmetic operators

OperatorDescription
+Adds two numbers.
-Subtracts two numbers.
*Multiplies two numbers.
/Divides two numbers.
%Computes the remainder after dividing two numbers.
^Raises the number to the specified power.

String operators

OperatorDescription
+Concatenate two strings.

Comparison operators

OperatorDescription
==true when two values are equal.
!=true when two values aren’t equal.
<true when the left value is less than the right value.
<=true when the left value is less than or equal to the right value.
>true when the left value is greater than the right value.
>=true when the left value is greater or equal to the right value.

You can apply the equality operators == and != to any operands.

The two operands in ordering operators < <= > and >= must both be orderable and of the same type. The results of the comparisons are:

  • Boolean values are equal if they’re either both true or both false.
  • Numerical (integer and floating-point) values are orderable in the usual way.
  • String values are orderable lexically byte-wise.
  • Objects are equal if all their fields are equal.
  • Array values are equal if their corresponding elements are equal.

Logical operators

OperatorDescription
&&true when the both left and right value are true.
||true when the either left or right value are true.
!Negates a boolean value.

Logical operators apply to boolean values and yield a boolean result.

Assignment operator

The Alloy configuration syntax uses = as its assignment operator.

An assignment statement may only assign a single value. Each value must be assignable to the attribute or object key.

  • You can assign null to any attribute.
  • You can assign numerical, string, boolean, array, function, capsule, and object types to attributes of the corresponding type.
  • You can assign numbers to string attributes with an implicit conversion.
  • You can assign strings to numerical attributes if they represent a number.
  • You can’t assign blocks.

Brackets

BracketsDescription
{ }Defines blocks and objects.
( )Groups and prioritizes expressions.
[ ]Defines arrays.

The following example uses curly braces and square brackets to define an object and an array.

alloy 
obj = { app = "alloy", namespace = "dev" }
arr = [1, true, 7 * (1+1), 3]

Access operators

OperatorDescription
[ ]Access a member of an array or object.
.Access a named member of an object or an exported field of a component.

You can access arbitrarily nested values with Alloy’s access operators. You can use square brackets to access zero-indexed array indices and object fields by enclosing the field name in double quotes. You can use the dot operator to access object fields without double quotes and component exports.

alloy 
obj["app"]
arr[1]

obj.app
local.file.token.content

If you use the [ ] operator to access a member of an object where the member doesn’t exist, the resulting value is null.

If you use the . operator to access a named member of an object where the named member doesn’t exist, an error is generated.