Value for non existent mapping

I have a mapping address to int. For addresses that are not in the mapping, what is the returned int value…0 or something else?

I guess it will actually throw an error? And I need to use something like state.myMapping[myAdr=0] if I want it to return 0 for addresses non existent in the mapping?

state.myMapping[myAdr=0] will return 0 as this is the syntax for providing a default value. state.myMapping[myAdr] will fail if there is no such key. Or Map.lookup(myAdr, state.myMapping) will return option(int) so you can decide what to if the key is not existent.


@philipp.chain - one more thing, something like state.myMapping[myAdr=1] will return 1 as expected, but say state.myMapping[myAdr=-1] does not compile. state.myMapping[myAdr=(-1)] compiles but doesn’t work. Is that intended behaviour? I would expect that negative numbers could be returned as well?

You need a space between the = and the - or the parser thinks it’s one token.
state.myMapping[myAdr=(-1)] works as expected for me.

/ Ulf

1 Like

I am using online IDEs ( and and seems both are having issues with CORS trying to reach remote compiler:
Cross-Origin Request Blocked: The Same Origin Policy disallows reading the remote resource at (Reason: CORS header ‘Access-Control-Allow-Origin’ missing).

I am using VIM and the command line compiler, that works just fine! :stuck_out_tongue:

haha yes, that is nice, but it would also be nice if online compiler worked as well, otherwise what is the point of having it :stuck_out_tongue:

@DinchoTodorov.chain can help here probably