E043: You're using this variable before you've actually created it

Turf runs your code from top to bottom, one statement at a time – so a variable has to be declared with mut or immut BEFORE you can use it, not after. This error means Turf found a real, valid declaration for the name you used… it’s just further down in the same block, after the line that tried to use it.

mut y: int = x + 1;   // x doesn't exist yet at this point!mut x: int = 5;       // x is only created here, one line too late

The fix is simply to reorder things so the declaration comes first:

mut x: int = 5;mut y: int = x + 1;   // now x already exists by the time we use it

This is an easy one to trip on when you’re moving code around or writing things in a different order than you first thought of them – nothing to worry about, just swap the two lines (or move the declaration up) and you’re done. If it turns out the name is a typo instead of a real ordering issue, Turf’s other unknown-name error will usually catch that case and suggest the right name instead.

Run turf --explain E043 in a terminal to read this again.