1. Suppose the OP did not take the source code files, but memorized the source code and later recalled it from memory. Would that be theft?
2. Suppose the OP neither took the file nor memorized the code, but had photographic memory and replayed the exact visual scenes during their creation of the utility functions and copied down the code from what they saw in their mind's eye. Would that be theft?
3. Suppose the OP was solving a seemingly novel problem and suddenly remembered how they solved the exact same problem when they were employed by company X. Are they obligated to banish this solution from their mind?
For the other examples, it depends but I'm pretty sure a copyright infringement case for either of them wouldn't be immediately thrown out. IANAL but I do know that law is quite fuzzy.
2. Suppose the OP neither took the file nor memorized the code, but had photographic memory and replayed the exact visual scenes during their creation of the utility functions and copied down the code from what they saw in their mind's eye. Would that be theft?
3. Suppose the OP was solving a seemingly novel problem and suddenly remembered how they solved the exact same problem when they were employed by company X. Are they obligated to banish this solution from their mind?