Help understanding UFC and templates

[ggibson]

Hi,

I still get tripped up by this. Why is it that some templates allow me to write 
using dot notation, and others do not? Is it that the ones that do not allow 
dot notation have untyped parameters? - Why would that affect it? My current 
workflow is to memorize the list of UFCable templates by trial and error, which 
is annoying. I'm hoping to find a better answer for when introducing nim to 
others.
    
    
    import sequtils, tables
    var a = {0:10,1:20,2:30}.toTable()
    withValue(a, 1, value) do: # OK function call use of template
        value[] = 11
    a.withValue(1, value) do: # OK method call use of template
        value[] = 11
    echo toSeq(a.pairs) # OK function call use of template
    echo a.pairs.toSeq() # ERROR method call use of template
    # maybe the dot notation with iterator is confusing the compiler...
    echo pairs(a).toSeq() # ERROR nope, still doesn't work
    
    
    Run

Thanks!