++ (and --) not supported on non-basic types

[shokrof]

I am trying to run this code, It can't be compiled and the status is just "Error" without any help messages.

Job Reference: http://boa.cs.iastate.edu/boa/?q=boa/job/82449

Robert informed me that the bug is in this line committers[node.author.username]++; and he suggests to change it to 'committers[node.author.username] = 1 + lookup(committers, node.author.username, 0);'

Thanks,
Moustafa

[neoblizz]

Are you using comitters as a map[string] of int? I have the exact same issue.

[psybers]

@neoblizz if you are using a map, you have to be sure the map contains the key you are trying to read before using that value. Otherwise the value is undefined, and it leads to problems later.

Code like this is much safer for reading a value from a map: lookup(m, k, defaultValue) as this will never fail. If the value is in the map you get it, otherwise you get the default.

[psybers]

This particular bug is specifically regarding the crash when using ++ on a non-basic type (things like a map).

[neoblizz]

@psybers and just to clarify, the default value is optional there, correct? So, if I wanted to get the value at k, I could just do lookup(m, k)?

[psybers]

@neoblizz no it is required. The default is what the lookup function returns if the key k is not already in the map. If it is in the map, it returns the value k maps to.