so wrote:
It doesn't matter what signature you use for the function, compiler is aware and will output an error when you do the opposite of the signature. If this is the case, why do we need that signature?
Examine the API of a function in a library. It says it doesn't modify anything reachable through its arguments, but is that true? How would you know? And how would you know if the API doc doesn't say?
You'd fall back to const by convention, and that is not reliable and does not scale. You have to manually go through an entire hierarchy of function calls to figure out if one might change a member of the data structure, and then after a few maintenance cycles, you have to do that all over again.
Or not, and just hope for the best (which is what happens in practice). The "why", then, is that guarantees are better than hope.
