3.1.3. Custom Operators

In addition to the standard Python operators, Caterpillar allows you to define custom operators tailored to specific use cases. These custom operators can be used to create more expressive and domain-specific syntax when defining structs and fields. For example, you can create an operator that automatically generates an array of a fixed length, making your code cleaner and more intuitive.

To define a custom operator, Caterpillar provides a mechanism using the _infix_ function, which allows you to wrap a lambda or function as an operator. This custom operator can then be applied to fields in a struct, just like any other operator.

Here’s an example that demonstrates how to define and use a custom operator:

from caterpillar.fields import _infix_

M = _infix_(lambda s, count: s[count * 2])

@struct
class Format:
    values: uint16 /M/ 3

• Pre-processing Stage: Custom operators are applied during the pre-processing phase. This means that they don’t directly affect the overall parsing or unpacking process. Instead, they modify the way a struct or field is defined before it is parsed. In the example above, the custom operator is used to modify the length of the array before the struct is processed.

• Return Custom Structs: Custom operators are useful for generating custom structs or configurations that simplify the definition of data layouts, especially when dealing with repetitive or dynamic patterns.

3.1.3.1. Limitations

While custom operators allow for a high degree of flexibility, they currently don’t modify the parsing process itself. Instead, they are primarily used to modify how fields or structs are defined before they are processed by the rest of the framework.