FileMaker Custom Functions

When to Abstract and When to Inline

You’re writing a calculation to format a phone number. You’ve done this before in three other places in your solution. Should you create a custom function called FormatPhoneNumber, or just write the calculation inline again?

A week later, you need a complex date calculation that you’ll only use once. Should you create a custom function for clarity, or keep it inline where it’s needed?

Knowing when to utilize a custom function is a solid skill to have in FileMaker develop as it promises reusability and clean code. On the other hand, inline calculations promise simplicity and transparency. I’m going to help break down the distinction and situations to look out for that will help lead you to pick one over the other.

Understanding the Trade-Off

Custom functions and inline calculations represent different philosophical approaches to organizing your code.

Inline calculations are transparent. When you look at a calculation field or script step, you see exactly what’s happening. No need to hunt through your function library to understand the logic. The calculation is self-contained and explicit.

Custom functions are abstract. They hide implementation details behind a…