#15 Passes literal instead of value to ctor expecting string

[Dan Ingold]

Given a class whose ctor takes a string, xParam does
not appear to correctly init the class with a literal (i.e.,
constant) parameter. xParam passes the name of the
constant to the ctor, rather than its value. For
example, the attached test program prints

Test contains "INIT"

rather than

Test contains "xyzzy"

I assume this occurs because under the relaxed syntax
rules, xParam interprets INIT as a string instead of a
constant. Shouldn't xParam look for the token in the
symbol table before presuming it is a string?

If I am missing some fundamental concept here, please
let me know. Thank you.

Regards,
Dan

[Dan Ingold]

Example code demonstrating bug

[Ronnie Maor]

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After checking the problem on my computer, I found two
relevant issues:

1) In the statement param_const("INIT",Test::INIT), the type
of Test::INIT is "const char *", so XParam tries to register
the constant, but can't finish the registeration since it waits
for the type "const char *" to be registered first (which never
happens, and shouldn't).
You can see this if you try to get help from XParam on the
topic "PENDING". One way to do this is give the following in
your argv: {"dummy", "! PENDING"}.
The solution is to copy the literal into a string, and give that
string as the parameter to param_const, or just convert to
string inline.

2) If you do the above, you'll still need to add an xparam_init
call before input() (best practice is having it as the first line
of main()). Otherwise XParam parses the string first, and only
performs the initialization (which executes the registration)
when it tries to build the value. At that point it has already
decided that INIT is a string and not a constant. The way to
see this is to call input() twice - you'll see that the second
time works, since the registration is triggered during the first
call.

This second issue is indeed a bug, so thanks. I hope we've
given you enough information to be able to circumvent it.

Ronnie