[jerf]

In addition to the 15 bytes used by the string itself, which will be rounded up to a minimum of 16 bytes in RAM (and probably larger), the string carries additional words for pointers and data, whereas the int is just 4 bytes and done. Go can use it as a value type so there doesn't even have to be another couple of words wrapping it as an "object" or something. Plus you can potentially start optimizing for the int case with various clever things more easily, because it's so tight it gets down into the realm where bit bashing games can be used to potentially avoid cache line hits, etc. whereas the string representation isn't so amenable to that.