how to pass default value and check if a key exist in toml file

[billcxx]

I see in the Getting started Tutorials,

The get_value interface for processing the TOML data structure ensures that the data structure is complete throughout the whole process of reading it and will add the requested nodes if there are not present or will fill them in with default values. Convince yourself that the empty table indeed changed while reading by passing a serializer to it.

But how can I pass the default value? In call get_value(child, "reverse", reverse, .false.), is the fourth argument the default value?

Another question, is it possible to check if a key exists in a toml table?

[awvwgk]

The (optional) fourth argument in the getter interface for tables is the default value.

Usually you do not need to explicitly check for presence. The has_key type bound procedure can be used, but I recommend the error handling recipe instead on ways to check directly using the getter interface.

[billcxx]

Thanks for the quick explanation. Sorry for my ignorance, but one more question, is the "error handling recipe" you mentioned referring to the stat optional argument in the get_value interface?

I see snippets like this in the How-Tos/Reporting errors

    call get_value(table, "timestep", config%timestep, 0.5, stat=stat, origin=origin)
    if (stat /= 0) then
      print '(a)', context%report("Cannot read timestep", &
        & origin, "expected real value")
      stop 1
    end if

[awvwgk]

I don't think there is an explicit recipe yet targeting this topic. The error reporting recipe does this touch a bit, also there are some mentions in the table handling recipe section.

If you have a specific use case it might be useful to add it to the recipes and describe how absent data is dealt with. However, the general design strategy of TOML Fortran's getter interface should allow to minimize the need to worry about the existence of keys or entries.

[billcxx]

Thanks for the explanation. I'm just thinking what I may need for the future, so I don't have an actual use case yet. I will create issue/PR for documentation if I meet and solve problems dealing with absent data in my program.