#81 No way to check if a map already contains a key

[Jacob Minsky]

There seems to be no way to check if a map key is defined. For example,

map a
a['c'] = 3
print a['b']

produces "ERROR on line 3: Map key does not exist.".

The problem is that there is no way to check if the key is defined before accessing it. That's a very big limitation on the use of map, it's not really possible to use it in most algorithms.

Proposal: we could make it work with code like

if typeof(a['b']) = type_unassigned then print "key not found"

Currently, this fails because the error would be thrown before the comparison. That can be fixed by removing the line
if (DataElement::getError()) {error->q(DataElement::getError(true),i);}
around line 1812 of Interpreter.cpp. This will let the returned element be of type type_unassigned and the typeof statement above would work. That's possibly not ideal, since we would also allow statements like c=a['no_key'] which would make c of unassigned type, so it would fail on a later line rather than immediately.

A more sophisticated implementation could allow a['no_key'] only within a typeof statement.

Thoughts? Or am I completely missing some way to check if a map has a key?

[Jacob Minsky]

After some searching in the code, I found that the "in" operator does what I want, e.g.

if not ('d' in a) then print "no such key"

Unfortunately this use of "in" is not documented, but as far as code changes, the issue can be closed.