REST vs RPC - *Actual purpose* differences -

i started writing web-apps , distributed apps when rest popular, never used rpc.

when searching simple explanation of difference between them, started understand, examples got me confused.
saw things this:

get /getlastuser 

or this:

post /changeusername 

if rest meant resources, , rpc meant procedures, isn't bad practice using rpc this?

correct me if i'm wrong, way see it, rpc should more purely functional.
meaning calling procedure should always:

• return same result same arguments
• not affect state

so, rpc calls this:

get /addtwo?num=5 

that return this:

{     "result": 7 } 

seem more logical me (although that's simple example).

if question gets closed being "opinion-based", i'll know should whatever heck want...

rpc not meant functional. calling same procedure twice gives no guarantee result.

this question can answered few different ways, , pretty deep. think might fair summary.

• with rpc primitives typically function names, arguments , results.
• with rest primitive 'resource representation'.

so rpc might call function, in rpc sending , retrieving state of resource, regardless of protocol.

this means typically ask server 'can give me state of resource', or tell server 'here's new resource state, please store @ location'. successful answers rest give "the current state" or "this operation worked", rpc question (function + arguments) , answer (the result) can anything.

so can argue when describe this, rpc lot more flexible. is, because rest confines transmitting state, gain lot of guarantees simple rpc-based protocol not give.

rest not transferring state. usage hyper-links important requirement service called rest, , don't 'out of box' rpc.

lastly, can argued http rpc-like protocol. think it's possible build restful service on top of rpc service.