sugar.collect doesn't work with string + other bugs

[timotheecour]

sugar.collect doesn't work with string
It's a special case but an important one.

Example 1

when true:
  import std/sugar
  let s = collect(newStringOfCap(4)):
    for j in 0..<4: char(j)

Current Output

Error: cannot instantiate: 'newStringOfCap[typeof:

Expected Output

works

Example 2

collect doesn't work with when

when true:
  import std/sugar
  let s = collect(newSeqOfCap(4)):
    when true:
      for j in 0..<4: char(j)
    else:
      for j in 0..<3: char(j)
  echo s

Additional Information

• devel 1.5.1 d9038ed
• also reported in forum TITLE: one more "collect" question (bug?) - Nim forum

[ringabout]

collect is a bit hacky, it only supports generics constructor now.

import std/sugar

proc newStringI[T](size: int): string =
  newStringOfCap(size)


let s = collect(newStringI(4)):
  for j in 55 ..< 59: char(j)

echo s

[timotheecour]

collect is a bit hacky, it only supports generics constructor now.

ya, and it seems hard/impossible to fix in a way that's not ambiguous, given that a symbol can have both generic and non-generic overloads. Hence #16082 which also offers other advantages

[Araq]

This works fine:

import sugar

proc newString[T: string](len: int): string = system.newString(len)

var st = collect(newString(3)):
  for i in 0..2: "this does not work"

echo st

[timotheecour]

this should work without having to introduce this overload, this is clunky.