array, seq : is there something in between?

[HJarausch]

Thanks, I'll have a look at wrapping `alloca`, but I am pessimistic:

The problem arose when I tried to return a _seq_ within a parallel for loop. I 
fear (currently) a **parallel for loop** doesn't work with custom types. Here 
is a slightly modified version of an example given by _ynfle_ which fails to 
compile
    
    
    import strutils, math, threadpool
    type
      Coeff = object
        c: array[1,float]
    
    proc term(k: int): Coeff =
      result = Coeff(c: [(if (k and 1) == 0 : 1.0 else: -1.0) * 4.0/(float(k+k) 
+ 1.0)])
    
    proc pi(n: int): float =
      var ch = newSeq[FlowVar[Coeff]](n+1)
      {.push experimental: "parallel".}
      parallel:
        for k in 0..ch.high:
          ch[k] = spawn term(k)
          #  type mismatch: got 'Coeff' for 'spawn term(k), nimCreateFlowVar' 
but expected 'FlowVar[Vx.Coeff]'
      for k in 0..ch.high:
        result += (^ch[k]).c[0]
      
      {.pop.}
    
    echo formatFloat(pi(5000))
    
    
    Run