Alternative to eval()

No. There isn't any alternative. Also. this is an undocumented function of Appian. As far as reason is concerned about why this is not generally available, lets wait to hear from someone from Appian. 

In reverse order:

• it's not best practice to use unsupported functions. eval() is unsupported:

• AFAIK there is no alternative. 

That answers your specific questions. Taking a step back - what is the actual problem you're trying to solve here?

I want to use it as such: 

eval(
  "updatedictionary(
    fv!item,
    {
      "&ri!pkName&": null
    }
  )"
)

where ri!pkName is a cdt field which i want to address in updatedictionary()

a!update should get you there.

eval() is evil! It allows an attacker to inject code into your application. Think of a SQL injection attack.

Oh thanks, that was helpful.