// following code compiles:

typedef struct {uint8_t x;} structType;
void setup() {}
void myFunc(structType structInstance){}
void loop() {}

// following code doesn't:

void setup() {}
typedef struct {uint8_t x;} structType;
void myFunc(structType structInstance){}
void loop() {}

// "test:4:13: error: variable or field 'myFunc' declared void"