Custom attributes?

Question

Is it possible to assign custom attributes to symbols and check them later?

SetAttributes[a, b]

says

Attributes::attnf: b is not a known attribute.

Answer 1

No, I do not believe it is. As the documentation for your error message says:

The attributes available in each version of Mathematica are fixed and cannot be changed.

The system attributes are low level properties that fundamentally change the evaluation of symbols. I think it makes sense that these are not mixed with high-level user constructs, even though at times that would be quite convenient.

For an alternative remember that you can attach Options to a symbol, e.g.:

Options[a] = {"Attributes" -> {"b"}};

OptionValue[a, "Attributes"]

{"b"}

You could also use a single DownValues rule such as:

a["Attributes"] = {"b"};

a["Attributes"]

{"b"}