E129: There is nothing to work the type out from

What compiler error E129 means, and how to fix it.

guess means “use whatever type the value on the right has”. That only works when the value has a real type to offer. Turf found one that doesn’t:

Example

mut a: guess = null;              // `null` could be a reference to anythingmut b: guess = print_it();        // print_it() returns void: no value, no typemut c: guess = List::default();   // which kind of List?

Say the type yourself, the same way you would without guess:

Example

mut a: &?Point = null;mut c: List<int> = List::default();

For the void case, the real problem is usually that the function was supposed to return something. Call it as a statement on its own if you only want what it does:

Example

print_it();

The same error is reported at a generic function whose type parameter no parameter mentions. Type arguments are worked out from the arguments of each call, and there is no way to write them yourself, so T here could never be decided:

Example

fn<T> make(): T { ... }           // which T would `make()` be?

Use the type parameter in a parameter (fn<T> make(seed: T): T), or drop it and name a real type.

Run turf --explain E129 in a terminal to read this again.