Why fmt doesn't work?

[alexeypetrushin]

Why string interpolation in code below fails with `Error: undeclared 
identifier: 'id'`? [play](https://play.nim-lang.org/#ix=4x8U)
    
    
    import std/strformat
    
    type Some* = object
      id*: string
    
    template somet(o: Some) =
      let id: string = o.id
      echo "id" & id    # works
      echo fmt"id {id}" # <= Error
    
    let o = Some()
    somet(o)
    
    
    Run