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Forums · BridgePoint/xtUML Usage and Training

Why does BridgePoint grammar allow ? as rval

Bob Mulvey · September 30, 2015 at 4:32 pm

In discussion today, the BP oal grammar was discussed (QMARK in https://github.com/xtuml/bridgepoint/blob/master/src/org.xtuml.bp.als.oal/bnf/oal.bnf ). Specifically, there is support for an rval of ? (qmark in oal.bnf). Looking at the current implementation for this token I see no valid use case. Furthermore, there is inconsistency between the parser and verifier here (parser allows something that the verifier does not support).

Consider:

Example 1 (this IS currently valid syntax AND executes): test=1; test=?; LOG::LogInteger(message:test); // This displays the value 1

Example 2 (this is valid syntax, but execution fails on the first assignment because there is no type defined type in BPValue::getValueString): test=?; test=1;

I could see where example 2 could be useful to allow syntax where there was an unknown value or even unknown type that was initialized later, for example:

example 3 (not supported by the parser): test=? if (test==?) test=1; else test=”string”; // parser error, type already defined end if;

Does anyone understand the history of why this rval “?” is present?

Lee Riemenschneider · May 17, 2017 at 3:41 pm

In this discussion, a workaround was shown for how to create an out-of-scope unassigned inst_ref variable. The QMARK seems to be what was put into OAL for this purpose with any type of data variable.

The problem with inst_ref is the QMARK variable can’t be used inside a select, so a workaround must still be used. ref = ?; if (true) select object instance foo of BAR; ref = foo; end if; if (empty ref) end if;

Verifier should probably support the QMARK. MC-3020 seemed to handle it OK in an experiment I ran.

In a discussion yesterday, Levi and I surmised that the proper handling of no assignment should be a default value for the type. e.g., ref = ?; if (false) select object instance foo of BAR; ref = foo; end if; ref will be empty here due to no assignment.